Your skin is your body's largest organ. It covers and protects your body. Your skin

• Holds body fluids in, preventing dehydration
• Keeps harmful microbes out, preventing infections
• Helps you feel things like heat, cold, and pain
• Keeps your body temperature even
• Makes vitamin D when the sun shines on it

Anything that irritates, clogs, or inflames your skin can cause symptoms such as redness, swelling, burning, and itching. Allergies, irritants, your genetic makeup, and certain diseases and immune system problems can cause rashes, hives, and other skin conditions. Many skin problems, such as acne, also affect your appearance.

Two common skin disorders are eczema and acne. Eczema is an inflammatory condition and occurs in individuals of all ages. Acne involves the clogging of pores, which can lead to infection and inflammation, and is often seen in adolescents. Other disorders, not discussed here, include seborrheic dermatitis (on the scalp), psoriasis, cold sores, impetigo, scabies, hives, and warts.

Eczema

Eczema is an allergic reaction that manifests as dry, itchy patches of skin that resemble rashes (Figure). It may be accompanied by swelling of the skin, flaking, and in severe cases, bleeding. Many who suffer from eczema have antibodies against dust mites in their blood, but the link between eczema and allergy to dust mites has not been proven. Symptoms are usually managed with moisturizers, corticosteroid creams, and immunosuppressants.

Eczema

Eczema is a common skin disorder that presents as a red, flaky rash. (credit: “Jambula” Wikimedia Commons / NIAID, Flickr)

Acne

Acne is a skin disturbance that typically occurs on areas of the skin that are rich in sebaceous glands (face and back). It is most common along with the onset of puberty due to associated hormonal changes, but can also occur in infants and continue into adulthood. Hormones, such as androgens, stimulate the release of sebum. An overproduction and accumulation of sebum along with keratin can block hair follicles. This plug is initially white. The sebum, when oxidized by exposure to air, turns black. Acne results from infection by acne-causing bacteria (Propionibacterium and Staphylococcus), which can lead to redness and potential scarring due to the natural wound healing process (Figure).

Acne

Acne is a result of over-productive sebaceous glands, which leads to formation of blackheads and inflammation of the skin.

Injuries

Because the skin is the part of our bodies that meets the world most directly, it is especially vulnerable to injury. Injuries include burns and wounds, as well as scars and calluses. They can be caused by sharp objects, heat, or excessive pressure or friction to the skin.

Skin injuries set off a healing process that occurs in several overlapping stages. The first step to repairing damaged skin is the formation of a blood clot that helps stop the flow of blood and scabs over with time. Many different types of cells are involved in wound repair, especially if the surface area that needs repair is extensive. Before the basal stem cells of the stratum basale can recreate the epidermis, fibroblasts mobilize and divide rapidly to repair the damaged tissue by collagen deposition, forming granulation tissue. Blood capillaries follow the fibroblasts and help increase blood circulation and oxygen supply to the area. Immune cells, such as macrophages, roam the area and engulf any foreign matter to reduce the chance of infection.

Burns

A burn results when the skin is damaged by intense heat, radiation, electricity, or chemicals. The damage results in the death of skin cells, which can lead to a massive loss of fluid. Dehydration, electrolyte imbalance, and renal and circulatory failure follow, which can be fatal. Burn patients are treated with intravenous fluids to offset dehydration, as well as intravenous nutrients that enable the body to repair tissues and replace lost proteins. Another serious threat to the lives of burn patients is infection. Burned skin is extremely susceptible to bacteria and other pathogens, due to the loss of protection by intact layers of skin.

Burns are sometimes measured in terms of the size of the total surface area affected. This is referred to as the “rule of nines,” which associates specific anatomical areas with a percentage that is a factor of nine (Figure). Burns are also classified by the degree of their severity. A first-degree burn is a superficial burn that affects only the epidermis. Although the skin may be painful and swollen, these burns typically heal on their own within a few days. Mild sunburn fits into the category of a first-degree burn. A second-degree burn goes deeper and affects both the epidermis and a portion of the dermis. These burns result in swelling and a painful blistering of the skin. It is important to keep the burn site clean and sterile to prevent infection. If this is done, the burn will heal within several weeks. A third-degree burn fully extends into the epidermis and dermis, destroying the tissue and affecting the nerve endings and sensory function. These are serious burns that may appear white, red, or black; they require medical attention and will heal slowly without it. A fourth-degree burn is even more severe, affecting the underlying muscle and bone. Oddly, third and fourth-degree burns are usually not as painful because the nerve endings themselves are damaged. Full-thickness burns cannot be repaired by the body, because the local tissues used for repair are damaged and require excision (debridement), or amputation in severe cases, followed by grafting of the skin from an unaffected part of the body, or from skin grown in tissue culture for grafting purposes.

Calculating the Size of a Burn

The size of a burn will guide decisions made about the need for specialized treatment. Specific parts of the body are associated with a percentage of body area.

Scars and Keloids

Most cuts or wounds, with the exception of ones that only scratch the surface (the epidermis), lead to scar formation. A scar is collagen-rich skin formed after the process of wound healing that differs from normal skin. Scarring occurs in cases in which there is repair of skin damage, but the skin fails to regenerate the original skin structure. Fibroblasts generate scar tissue in the form of collagen, and the bulk of repair is due to the basket-weave pattern generated by collagen fibers and does not result in regeneration of the typical cellular structure of skin. Instead, the tissue is fibrous in nature and does not allow for the regeneration of accessory structures, such as hair follicles, sweat glands, or sebaceous glands.

Sometimes, there is an overproduction of scar tissue, because the process of collagen formation does not stop when the wound is healed; this results in the formation of a raised or hypertrophic scar called a keloid. In contrast, scars that result from acne and chickenpox have a sunken appearance and are called atrophic scars.

Scarring of skin after wound healing is a natural process and does not need to be treated further. Application of mineral oil and lotions may reduce the formation of scar tissue. However, modern cosmetic procedures, such as dermabrasion, laser treatments, and filler injections have been invented as remedies for severe scarring. All of these procedures try to reorganize the structure of the epidermis and underlying collagen tissue to make it look more natural.

Bedsores and Stretch Marks

Skin and its underlying tissue can be affected by excessive pressure. One example of this is called a bedsore. Bedsores, also called decubitis ulcers, are caused by constant, long-term, unrelieved pressure on certain body parts that are bony, reducing blood flow to the area and leading to necrosis (tissue death). Bedsores are most common in elderly patients who have debilitating conditions that cause them to be immobile. Most hospitals and long-term care facilities have the practice of turning the patients every few hours to prevent the incidence of bedsores. If left untreated by removal of necrotized tissue, bedsores can be fatal if they become infected.

The skin can also be affected by pressure associated with rapid growth. A stretch mark results when the dermis is stretched beyond its limits of elasticity, as the skin stretches to accommodate the excess pressure. Stretch marks usually accompany rapid weight gain during puberty and pregnancy. They initially have a reddish hue, but lighten over time. Other than for cosmetic reasons, treatment of stretch marks is not required. They occur most commonly over the hips and abdomen.

Calluses

When you wear shoes that do not fit well and are a constant source of abrasion on your toes, you tend to form a callus at the point of contact. This occurs because the basal stem cells in the stratum basale are triggered to divide more often to increase the thickness of the skin at the point of abrasion to protect the rest of the body from further damage. This is an example of a minor or local injury, and the skin manages to react and treat the problem independent of the rest of the body. Calluses can also form on your fingers if they are subject to constant mechanical stress, such as long periods of writing, playing string instruments, or video games. A corn is a specialized form of callus. Corns form from abrasions on the skin that result from an elliptical-type motion.

The integumentary system is susceptible to a variety of diseases, disorders, and injuries. These range from annoying but relatively benign bacterial or fungal infections that are categorized as disorders, to skin cancer and severe burns, which can be fatal. In this section, you will learn several of the most common skin conditions.

Diseases

One of the most talked about diseases is skin cancer. Cancer is a broad term that describes diseases caused by abnormal cells in the body dividing uncontrollably. Most cancers are identified by the organ or tissue in which the cancer originates. One common form of cancer is skin cancer. The Skin Cancer Foundation reports that one in five Americans will experience some type of skin cancer in their lifetime. The degradation of the ozone layer in the atmosphere and the resulting increase in exposure to UV radiation has contributed to its rise. Overexposure to UV radiation damages DNA, which can lead to the formation of cancerous lesions. Although melanin offers some protection against DNA damage from the sun, often it is not enough. The fact that cancers can also occur on areas of the body that are normally not exposed to UV radiation suggests that there are additional factors that can lead to cancerous lesions.

In general, cancers result from an accumulation of DNA mutations. These mutations can result in cell populations that do not die when they should and uncontrolled cell proliferation that leads to tumors. Although many tumors are benign (harmless), some produce cells that can mobilize and establish tumors in other organs of the body; this process is referred to as metastasis. Cancers are characterized by their ability to metastasize.

Basal Cell Carcinoma

Basal cell carcinoma is a form of cancer that affects the mitotically active stem cells in the stratum basale of the epidermis. It is the most common of all cancers that occur in the United States and is frequently found on the head, neck, arms, and back, which are areas that are most susceptible to long-term sun exposure. Although UV rays are the main culprit, exposure to other agents, such as radiation and arsenic, can also lead to this type of cancer. Wounds on the skin due to open sores, tattoos, burns, etc. may be predisposing factors as well. Basal cell carcinomas start in the stratum basale and usually spread along this boundary. At some point, they begin to grow toward the surface and become an uneven patch, bump, growth, or scar on the skin surface (Figure). Like most cancers, basal cell carcinomas respond best to treatment when caught early. Treatment options include surgery, freezing (cryosurgery), and topical ointments (Mayo Clinic 2012).

Basal Cell Carcinoma

Basal cell carcinoma can take several different forms. Similar to other forms of skin cancer, it is readily cured if caught early and treated. (credit: John Hendrix, MD)

Squamous Cell Carcinoma

Squamous cell carcinoma is a cancer that affects the keratinocytes of the stratum spinosum and presents as lesions commonly found on the scalp, ears, and hands (Figure). It is the second most common skin cancer. The American Cancer Society reports that two of 10 skin cancers are squamous cell carcinomas, and it is more aggressive than basal cell carcinoma. If not removed, these carcinomas can metastasize. Surgery and radiation are used to cure squamous cell carcinoma.

Squamous Cell Carcinoma

Squamous cell carcinoma presents here as a lesion on an individual’s nose. (credit: the National Cancer Institute)

Melanoma

A melanoma is a cancer characterized by the uncontrolled growth of melanocytes, the pigment-producing cells in the epidermis. Typically, a melanoma develops from a mole. It is the most fatal of all skin cancers, as it is highly metastatic and can be difficult to detect before it has spread to other organs. Melanomas usually appear as asymmetrical brown and black patches with uneven borders and a raised surface (Figure). Treatment typically involves surgical excision and immunotherapy.

Melanoma

Melanomas typically present as large brown or black patches with uneven borders and a raised surface. (credit: the National Cancer Institute / Centers for Disease Control)

Doctors often give their patients the following ABCDE mnemonic to help with the diagnosis of early-stage melanoma. If you observe a mole on your body displaying these signs, consult a doctor.

• Asymmetry – the two sides are not symmetrical
• Borders – the edges are irregular in shape
• Color – the color is varied shades of brown or black
• Diameter – it is larger than 6 mm (0.24 in)
• Evolving – its shape has changed

Some specialists cite the following additional signs for the most serious form, nodular melanoma:

• Elevated – it is raised on the skin surface
• Firm – it feels hard to the touch
• Growing – it is getting larger

What do your bumps, blisters, and blotches mean?

Skin: It's our body's largest organ. It protects us by keeping fluids in and harmful microbes out.

Sometimes, due to our environments and genes, our skin gets, well, unhappy. But how can you tell the difference between a minor rash and a more serious condition? Read our quick rundown of five common skin conditions and what they look like. Also, be sure to talk to a dermatologist, a doctor who specializes in skin conditions, or other health care provider for a full diagnosis and care.

Hives

Hives are pink, itchy bumps that can appear anywhere on the skin and last for less than 24 hours. They may be caused by some food allergy, infection, or medications. Hives are common and often go away on their own.

Eczema

Eczema, or atopic dermatitis, often begins before age 5 and may continue as kids get older. For some people, the raw, sensitive, and inflamed skin may cause severe itching at night. It often happens on the face, inside the elbows, behind the knees, and on the hands and feet.

Contact dermatitis

Contact dermatitis may have well-defined borders and appears when your skin touches a foreign substance (dyes, soaps, latex, poisonous plants). The resulting rash may be itchy and red, and oozing blisters may develop. The reaction most often occurs 24 to 48 hours after the exposure.

Psoriasis

Psoriasis consists of thick patches of rough, scaly skin, most commonly on the scalp, elbows, knees, and lower back. These patches can be itchy and painful and may bleed when scratched. Psoriasis sometimes runs in families and can be associated with arthritis that often involves the fingers, toes, or spine.

Dry skin

Dry skin occurs when your skin loses too much water and oil. It can happen at any age. The rough, cracked, and itchy skin may be caused by cold, dry air; washing your hands often; harsh soaps or detergents; and aging. As we get older, our skin makes less natural oil.

Have you ever had a skin rash that did not respond to over-the-counter creams, or a mole that you were concerned about? Dermatologists help patients with these types of problems and more, on a daily basis. Dermatologists are medical doctors who specialize in diagnosing and treating skin disorders. Like all medical doctors, dermatologists earn a medical degree and then complete several years of residency training. In addition, dermatologists may then participate in a dermatology fellowship or complete additional, specialized training in a dermatology practice. If practicing in the United States, dermatologists must pass the United States Medical Licensing Exam (USMLE), become licensed in their state of practice, and be certified by the American Board of Dermatology.

Most dermatologists work in a medical office or private-practice setting. They diagnose skin conditions and rashes, prescribe oral and topical medications to treat skin conditions, and may perform simple procedures, such as mole or wart removal. In addition, they may refer patients to an oncologist if skin cancer that has metastasized is suspected. Recently, cosmetic procedures have also become a prominent part of dermatology. Botox injections, laser treatments, and collagen and dermal filler injections are popular among patients, hoping to reduce the appearance of skin aging.

Dermatology is a competitive specialty in medicine. Limited openings in dermatology residency programs mean that many medical students compete for a few select spots. Dermatology is an appealing specialty to many prospective doctors, because unlike emergency room physicians or surgeons, dermatologists generally do not have to work excessive hours or be “on-call” weekends and holidays. Moreover, the popularity of cosmetic dermatology has made it a growing field with many lucrative opportunities. It is not unusual for dermatology clinics to market themselves exclusively as cosmetic dermatology centers, and for dermatologists to specialize exclusively in these procedures.

Consider visiting a dermatologist to talk about why he or she entered the field and what the field of dermatology is like.

Many people with skin conditions often turn to complementary health approaches, particularly vitamin, mineral, and herbal supplements. In spite of interest in complementary approaches, there have been only a few studies on complementary health approaches for skin conditions, and those that have been conducted have often had methodological problems. Here are 6 things you should know about complementary health approaches for skin conditions, including atopic dermatitis, psoriasis, acne, impetigo, and rosacea:

1. There is some limited evidence that relaxation techniques may help improve symptoms of atopic dermatitis, particularly in the pediatric population, although most studies have had problems with their methodology. The American Academy of Dermatology’s clinical practice guidelines for the treatment of atopic dermatitis has stated that there is inconsistent to no evidence to recommend the use of vitamins, minerals and herbal supplements. The guidelines also state that the use of probiotics/prebiotics for the treatment of patients with established atopic dermatitis is not recommended because of inconsistent evidence.

2. There is some evidence that fish oil, Dead Sea climatotherapy, and the topical herbs Mahonia aquifolium and indigo naturalis may be beneficial for the treatment of psoriasis.

3. According to the American Academy of Dermatology’s clinical practice guidelines for the treatment of acne, there are currently very limited data regarding the safety and efficacy of herbal and other complementary therapies such as topical tea tree oral or bee venom to recommend their use.

4. There is insufficient evidence to either recommend or dismiss herbal treatments for impetigo, including tea tree oil, garlic, coconut oils, tea effusions, and Manuka honey.

5. Although some natural products have shown promise for improving symptoms of rosacea, there is insufficient evidence to support the use of many of these products for rosacea.

6. Take charge of your health—talk with your health care providers about any complementary health approaches you use. Together, you can make shared, well-informed decisions.

People say that beauty’s only skin deep; it’s what’s on the “inside” that counts. Our insides are certainly important, but skin is your first layer of defense against the outside world. Skin can also give important clues to your overall health. Learn to take good care of your skin, so your skin can keep taking good care of you.

Skin protects your body in many ways. “The skin provides a barrier to protect the body from invasion by bacteria and other possible environmental hazards that can be dangerous for human health,” says NIH dermatologist Dr. Heidi Kong.

Skin plays other roles, too. It contains nerve endings that let you feel when an object is too hot or sharp, so you can quickly pull away. Sweat glands and tiny blood vessels in your skin help to control your body temperature. And cells in your skin turn sunlight into vitamin D, which is important for healthy bones.

Skin can also alert you to a health problem. A red, itchy rash might signal allergies or infections, and a red “butterfly” rash on your face might be a sign of lupus. A yellow tint might indicate liver disease. And dark or unusual moles might be a warning sign of skin cancer. Be on the lookout for unexpected changes to your skin, and talk with your doctor if you have concerns.

Your skin can become too dry if you don’t drink enough fluids or spend too much time in sunny or dry conditions. “While washing hands is important for good hygiene, washing your hands too much can also lead to dry skin,” Kong says, especially if you wash with hot water and harsh soaps. To treat dry skin, use moisturizing creams or lotions, and use warm instead of hot water when you bathe and wash your hands. You can also try using a humidifier to make the air in your home less dry.

The sun can damage your skin as well. Sunlight contains ultraviolet (UV) light that causes sunburn and makes your skin age faster, leading to more wrinkles as you get older. “There’s a strong link between UV exposure and skin cancer,” Kong adds. So protect your skin from the sun. Wear hats and other protective clothing, use sunscreen with a sun protection factor (SPF) of at least 30, and restrict your time in the sun during the late morning and early afternoon hours, when sunlight is strongest.

Many skin researchers like Kong are studying the skin’s microbiome—the bacteria and other microscopic organisms that live on your skin. Some of these microbes can be helpful. Evidence suggests that they boost the body’s infection-fighting immune system and help keep you healthy. “But there are some skin diseases with known associations with certain microbes,” says Kong. “We’re trying to understand how those microbes differ between healthy people and people with skin diseases.” In the long run, scientists would like to find ways to support healthy skin microbes while reducing harmful ones.

For tips to keep your skin healthy, see the “Wise Choices” box.

Tips for Healthy Skin

• Wash up. Bathe in warm—not hot—water; use mild cleansers that don’t irritate; and wash
  gently—don’t scrub.
• Block sun damage. Avoid intense sun exposure, use sunscreen, and wear protective clothing.
• Don’t use tanning beds or sunlamps. They emit the same harmful UV radiation as the sun.
• Avoid dry skin. Drink plenty of water, and use gentle moisturizers, lotions, or creams.
• Reduce stress. Stress can harm your skin and other body systems.
• Get enough sleep. Experts recommend about 9 hours a night for teens and 7-8 hours for adults.
• Speak up. Talk to your doctor if you notice any odd changes to your skin, like a rash or mole that changes size or color.

Blisters are fluid-filled sacs on the outer layer of your skin. They form because of rubbing, heat, or diseases of the skin. They are most common on your hands and feet.

Other names for blisters are vesicles (usually for smaller blisters) and bulla (for larger blisters).

Although you may not typically think of the skin as an organ, it is in fact made of tissues that work together as a single structure to perform unique and critical functions. The skin and its accessory structures make up the integumentary system , which provides the body with overall protection. The skin is made of multiple layers of cells and tissues, which are held to underlying structures by connective tissue (image). The deeper layer of skin is well vascularized (has numerous blood vessels). It also has numerous sensory, and autonomic and sympathetic nerve fibers ensuring communication to and from the brain.

Overview

The skin is composed of two major layers: a superficial epidermis and a deeper dermis. The epidermis consists of several layers beginning with the innermost (deepest) stratum basale (germinatum), followed by the stratum spinosum, stratum granulosum, stratum lucidum (when present), and ending with the outermost layer, the stratum corneum. The topmost layer, the stratum corneum, consists of dead cells that shed periodically and is progressively replaced by cells formed from the basal layer. The stratum basale also contains melanocytes, cells that produce melanin, the pigment primarily responsible for giving skin its color. Melanin is transferred to keratinocytes in the stratum spinosum to protect cells from UV rays.

The dermis connects the epidermis to the hypodermis, and provides strength and elasticity due to the presence of collagen and elastin fibers. It has only two layers: the papillary layer with papillae that extend into the epidermis and the lower, reticular layer composed of loose connective tissue. The hypodermis, deep to the dermis of skin, is the connective tissue that connects the dermis to underlying structures; it also harbors adipose tissue for fat storage and protection.

Your scalp is the skin on the top of your head. Unless you have hair loss, hair grows on your scalp. Different skin problems can affect your scalp.

Dandruff is a flaking of the skin. The flakes are yellow or white. Dandruff may make your scalp feel itchy. It usually starts after puberty, and is more common in men. Dandruff is usually a symptom of seborrheic dermatitis, or seborrhea. It is a skin condition that can also cause redness and irritation of the skin.

Most of the time, using a dandruff shampoo can help control your dandruff. If that does not work, contact your health care provider.

There is a type of seborrheic dermatitis that babies can get. It is called cradle cap. It usually lasts a few months, and then goes away on its own. Besides the scalp, it can sometimes affect other parts of the body, such as the eyelids, armpits, groin, and ears. Normally, washing your baby's hair every day with a mild shampoo and gently rubbing their scalp with your fingers or a soft brush can help. For severe cases, your health care provider may give you a prescription shampoo or cream to use.

Other problems that can affect the scalp include

• Scalp ringworm, a fungal infection that causes itchy, red patches on your head. It can also leave bald spots. It usually affects children.
• Scalp psoriasis, which causes itchy or sore patches of thick, red skin with silvery scales. About half of the people with psoriasis have it on their scalp.

A chronic inflammatory disease of the skin with unknown etiology. It is characterized by moderate ERYTHEMA, dry, moist, or greasy (SEBACEOUS GLAND) scaling and yellow crusted patches on various areas, especially the scalp, that exfoliate as dandruff. Seborrheic dermatitis is common in children and adolescents with HIV INFECTIONS.

The outer covering of the calvaria. It is composed of several layers: SKIN; subcutaneous connective tissue; the occipitofrontal muscle which includes the tendinous galea aponeurotica; loose connective tissue; and the pericranium (the PERIOSTEUM of the SKULL).

Eczema is a term for several different types of skin swelling. Eczema is also called dermatitis. Most types cause dry, itchy skin and rashes on the face, inside the elbows and behind the knees, and on the hands and feet. Scratching the skin can cause it to turn red, and to swell and itch even more.

Eczema is not contagious. The cause is not known. It is likely caused by both genetic and environmental factors. Eczema may get better or worse over time, but it is often a long-lasting disease. People who have it may also develop hay fever and asthma.

The most common type of eczema is atopic dermatitis. It is most common in babies and children but adults can have it too. As children who have atopic dermatitis grow older, this problem may get better or go away. But sometimes the skin may stay dry and get irritated easily.

Treatments may include medicines, skin creams, light therapy, and good skin care. You can prevent some types of eczema by avoiding

• Things that irritate your skin, such as certain soaps, fabrics, and lotions
• Stress
• Things you are allergic to, such as food, pollen, and animals

Eczema, or atopic dermatitis, is an inflammatory skin condition that affects an estimated 30 percent of the U.S. population, mostly children and adolescents. It is a chronic disease characterized by dry, itchy skin that can weep clear fluid when scratched. People with eczema also may be particularly susceptible to bacterial, viral, and fungal skin infections.

Impetigo is a skin infection caused by bacteria. It is usually caused by staphylococcal (staph) bacteria, but it can also be caused by streptococcal (strep) bacteria. It is most common in children between the ages of two and six. It usually starts when bacteria get into a break in the skin, such as a cut, scratch, or insect bite.

Symptoms start with red or pimple-like sores surrounded by red skin. These sores can be anywhere, but usually they occur on your face, arms and legs. The sores fill with pus, then break open after a few days and form a thick crust. They are often itchy, but scratching them can spread the sores.

Impetigo can spread by contact with sores or nasal discharge from an infected person. You can treat impetigo with antibiotics.