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.

Blisters often happen when there is friction - rubbing or pressure - on one spot. For example, if your shoes don't fit quite right and they keep rubbing part of your foot. Or if you don't wear gloves when you rake leaves and the handle keeps rubbing against your hand. Other causes of blisters include

• Burns
• Sunburn
• Frostbite
• Eczema
• Allergic reactions
• Poison ivy, oak, and sumac
• Autoimmune diseases such as pemphigus
• Epidermolysis bullosa, an illness that causes the skin to be fragile
• Viral infections such as varicella zoster (which causes chickenpox and shingles) and herpes simplex (which causes cold sores)
• Skin infections including impetigo

Blisters will usually heal on their own. The skin over the blister helps keep out infections. You can put a bandage on the blister to keep it clean. Make sure that there is no more rubbing or friction on the blister.

You should contact your health care provider if

• The blister looks infected - if it is draining pus, or the area around the blister is red, swollen, warm, or very painful
• You have a fever
• You have several blisters, especially if you cannot figure out what is causing them
• You have health problems such as circulation problems or diabetes

Normally you don't want to drain a blister, because of the risk of infection. But if a blister is large, painful, or looks like it will pop on its own, you can drain the fluid.

There are some things you can do to prevent friction blisters:

• Make sure that your shoes fit properly
• Always wear socks with your shoes, and make sure that the socks fit well. You may want to wear socks that are acrylic or nylon, so they keep moisture away from your feet.
• Wear gloves or protective gear on your hands when you use any tools or sports equipment that cause friction.