Cellulitis is an infection of the skin and deep underlying tissues. Group A strep (streptococcal) bacteria are the most common cause. The bacteria enter your body when you get an injury such as a bruise, burn, surgical cut, or wound.

Symptoms include

• Fever and chills
• Swollen glands or lymph nodes
• A rash with painful, red, tender skin. The skin may blister and scab over.

Your health care provider may take a sample or culture from your skin or do a blood test to identify the bacteria causing infection. Treatment is with antibiotics. They may be oral in mild cases, or intravenous (by IV) for more severe cases.

Erysipelas and cellulitis are skin infections that can develop if bacteria enter the skin through cuts or sores. Both infections make your skin swell, become red and tender. Erysipelas (also known as St. Anthony's fire) usually only affects the uppermost layers of skin, while cellulitis typically reaches deeper layers of tissue. Provided the right treatment is started early enough, these infections usually clear up without any lasting effects. Left untreated, they sometimes lead to serious complications.

Despite having a similar name, cellulitis has nothing to do with the more widely known but harmless “cellulite.”

Erysipelas and cellulitis are among the most common skin conditions, but it's not known exactly how often they occur. According to some studies, 2 out of 10,000 people are affected each year. Other research suggests that more than 250 out of 10,000 people are affected.

There are two main types of bacterial skin infections:

• Erysipelas
• Cellulitis (deeper infection of the connective tissue)

Both infections are most common on the feet or lower legs, but they may also affect other parts of the body. Erysipelas can develop on the face, and cellulitis may also occur on the palm of the hand, for instance. There it can spread in a V-shape in the tendon sheaths between the thumb, wrist and little finger.

Erysipelas affects the upper layers of the skin. The typical symptom is a painful and shiny light-red swelling of a quite clearly defined area of skin. Red streaks leading from that area may be a sign that the infection has started to spread along the lymph vessels too. In more severe cases, blisters may form as well. Nearby lymph nodes sometimes swell up and become more sensitive to pressure. People usually have a fever and generally feel unwell right from the start of the infection, when the skin first turns red.

In cellulitis, the reddened skin is less clearly defined than it is in erysipelas, and it is often dark-red or slightly purplish. Unlike erysipelas, the infection caused by cellulitis reaches the lower layers of skin and the tissue beneath it. The infection can spread along tendons and muscles, and pus may form.

Pain and swelling in the infected skin and connective tissue are typical of both forms. Fever and generally feeling ill are more common in erysipelas, but can also occur in severe cellulitis.

Erysipelas is often caused by streptococcus bacteria, while cellulitis is typically caused by Staphylococcus bacteria. Both types of bacteria may cause either erysipelas or cellulitis, though.

Bacterial skin infections are more likely to arise if the surface of your skin is damaged, making it easier for bacteria to enter. Because of this, the risk factors include skin problems such as eczema, impetigo, fungal infections such as athlete's foot, or wounds and ulcers. Erysipelas or cellulitis can also develop following injuries, pin pricks, and insect or animal bites, or if germs get into the wound during an operation.

The risk of infection is particularly high if you have a weakened immune system. The immune system may become weaker due to things like taking certain medications. These include some cancer drugs, corticosteroids and medication commonly used following organ transplants to suppress the body's immune response.

The risk is also higher in people who are overweight or have diabetes, problems with the circulation of lymph or blood, or have venous insufficiency. Previous erysipelas or cellulitis is considered to be a risk factor too.

Untreated bacterial skin infections can cause various complications. These include the following:

• The spread of pus-producing infection and abscesses: Especially in cellulitis, an infection with pus can spread to deeper tissue (such as muscle tissue). Sometimes the pus builds up in natural spaces or gaps between tissue. An abscess is a sealed, pus-filled space that can develop as a result of various bacterial skin infections. It is mostly made up of dead germs, tissue cells, and immune system cells.
• Lymphedema: Parts of the infected lymphatic vessels may be destroyed following an erysipelas infection. This blocks the flow of lymph (the fluid in the lymphatic system), causing it to build up. That results in permanent swelling and poorer circulation in the tissue, increasing the risk of developing further bacterial skin infections.

Life-threatening complications are rare. If bacteria enter the bloodstream, they may cause blood poisoning (septicemia). In rare cases, a bacterial skin infection on the face can cause meningitis(inflammation of the membranes covering the brain and spinal cord) or a blood clot in one of the blood vessels in the brain (cerebral venous thrombosis).

If there are complications, only fast treatment can prevent more major damage. Signs of a more severe infection include the following:

• Severe pain
• Fever, cold sweats, pale skin
• Nausea
• Faster rate of breathing or a racing heart
• Drowsiness, confusion, or other problems with consciousness or awareness

If you notice any of these symptoms, it is important to call the emergency services immediately.

Doctors can usually tell whether an infection is erysipelas or cellulitis based on the typical symptoms and the appearance of the skin. Your medical history or recent injuries often help to diagnose the problem too.

Further tests aren't usually needed. It can sometimes help to test fluid from the wound for germs. This is done when doctors think there may be a specific germ causing the infection, for instance, because someone’s skin became infected after they were bitten by an animal.

Erysipelas and cellulitis are both treated with antibiotics. The medication is delivered directly into a vein using a drip. In milder cases, tablets are enough. People who go to the hospital for treatment usually have to stay for about a week.

The exact type of antibiotic will depend on several factors, such as what type of bacteria doctors think you have. To check the progress of the treatment, the infected area of skin is outlined with a special marker pen. This makes it possible to see whether the antibiotics are having an effect and the infection and redness are going away.

It is also recommended that you cool the swelling and apply moist antiseptic wraps. Anti-inflammatory painkillers like ibuprofen can be used to relieve pain and fever.

If the skin on your face is infected, it's better to speak or chew as little as possible. If the skin on a leg or foot is infected, it can help to elevate that leg. Bed rest is even recommended in many cases. People are then given injections to prevent thrombosis.

In more severe cellulitis, surgery may be needed to remove pus and dead tissue

People who have had erysipelas or cellulitis are quite likely to develop the same kind of infection again after completing successful treatment. About one-third of people who have had an erysipelas infection get it again.

There are various ways to stop this from happening. If a skin condition like athlete’s foot or eczema made it easier for the infection to occur in the first place, it is important to treat this cause first. Also, it's important for people who have an increased risk of infection due to diabetes or circulation problems to pay attention to maintaining good foot hygiene.

If bacterial skin infections keep occurring, preventive treatment with antibiotics may be considered. When used for this purpose, the antibiotics need to be taken daily over the course of several months.