Blister

# Overview
A blister is a small pocket of fluid within the upper layers of the skin. Blisters can be filled with blood (known as blood blisters) or with pus (if they become infected). However, most blisters are filled with a clear fluid called serum. Serum is the part of the blood that remains after red blood cells and clotting agents have been removed.
A blister usually forms because the outer layer of the skin has become damaged. Fluid collects under the damaged layer of skin, cushioning the tissue underneath, protecting it from further damage and allowing it to heal.
A blood-blister usually forms when a small blood vessel close to the surface of the skin ruptures (breaks) and blood leaks into a tear between the layers of skin. This can happen if the skin is crushed, pinched or squeezed very tightly.
Blisters can also form as the result of certain medical conditions.

# Causes
Blisters are usually caused by injury to the skin from heat (for example from sunburn or a scald) or from friction.
Friction or heat on the skin can create a tear between the upper layer of the skin (the epidermis) and the layers beneath. When this happens the surface of the skin remains intact, but is pushed outwards as serum seeps into the newly created space between the layers.
Any rubbing of the skin can cause a blister if it is continued for long enough. Short periods of intense rubbing can also cause a blister. Blisters are most common on the hands and feet, as these parts of your body may rub against shoes or handheld equipment. Blisters form more easily on moist skin than on dry or soaked skin, and are more common in warm conditions.
Sometimes, the skin can blister when it comes into contact with a cosmetic, detergent, solvent or other chemical. This is known as contact dermatitis. Blisters can also develop as a result of an allergic reaction to an insect bite or sting.
There are a number of medical conditions that cause blisters. The most common are:
- chickenpox,
- herpes,
- impetigo, and,
- a form of eczema called pompholyx.
Other, much rarer conditions that cause blisters include:
- Bullous pemphigoid - a skin disease that causes large, tightly-filled blisters to develop. The disease usually affects people over the age of 60.
- Pemphigus - a serious skin disease in which blisters develop if pressure is applied to the skin. The blisters burst easily, leaving raw areas that can become infected.
- Dermatitis herpetiformis - a skin disease that causes intensely itchy blisters, usually on the elbows, knees, back and buttocks. The blisters usually develop in patches of the same shape and size on both sides of the body.
- Chronic bullous dermatosis of childhood - a disease that causes clusters of blisters on the face, mouth or genitals.

## Causes by Organ System

## Causes in Alphabetical Order

# Prevention
You can prevent blisters on your feet by wearing comfortable, well-fitting shoes and clean socks that you change daily. Blisters are more likely to develop on skin that is moist, so if you have particularly sweaty feet you may find wearing moisture-absorbing socks or changing your socks twice a day, necessary to prevent blisters. If you are exercising or playing sport, special sports socks can help keep your feet drier and reduce the chance of a blister.
Before going for a long walk, make sure that the shoes you are planning to wear have been broken in. If you do become aware of a hot area on your foot when walking, exercising or playing sport, stop immediately and tape some padding over the area.
To avoid blisters on your hands, wear work gloves when using tools such as a shovel or pickaxe, and when doing manual work such as gardening. You should also wear gloves when handling detergents, cleaning products, solvents and other chemicals.
To avoid friction to make a tear between the upper skin layer and the layers beneath one has to prevent friction forces being transmitted to the upper skin. This can be attained with a lubricant, typically talcum powder. Wearing gloves with talcum powder inside makes hands almost immune to blisters. The same goes for feet in shoes with talcum powder inside.
You should use sunscreen and cover up during the hottest part of the day to avoid blisters from sunburn. Moisturising, after-sun or calamine lotions can help to ease the discomfort if you do get burnt.

# Treatment
Most blisters heal naturally and do not require medical attention. As new skin grows beneath the blister, the fluid contained within it will be slowly reabsorbed by your body and the skin on top will dry and peel off.
The unbroken skin over a blister provides a natural barrier to infection. This means that you should try to keep blisters intact and unbroken in order to avoid infection. Try not to pierce a blister with a needle, but allow it to break on its own once the skin underneath has healed. If the blister is in a place (such as a hand or foot) that makes it extra painful, follow these steps:
1. Wash your hands and the blister with soap and water, and stearalize the blister with rubbing alcohol.
2. Steralize a pin with rubbing alcohol.
3. Make small pinpricks on the edge of the blister and drain the fluid through these.
4. Cover the blister with first-aid ointment and a sterile bandage.
Cover small blisters with a plaster (adhesive dressing). Larger blisters should be covered with a gauze pad or dressing that you can then tape in place. If you have a blister in a position that is causing you pain or that makes it likely to burst (such as on the sole of your foot), its important to cover it with a soft dressing to pad and protect it. Then change the dressing daily.
If a blister bursts, don't peel off the dead skin on top of the blister. Gently press the area to get rid of all the fluid inside, and then cover the blister and the area around it with a dry, sterile dressing to protect it from infection until it heals.
Blood blisters should also be left to heal naturally. As with other blisters, if a blood blister bursts it is important to keep the area clean and dry, and protect it with a sterile dressing to prevent infection.
Blood blisters are often painful, and you may wish to apply an ice pack to the area immediately after the injury that caused it. You should apply the ice pack for between 10 and 30 minutes. The ice should not touch your skin directly as this may cause a cold burn, so place a towel over the injured part first.
Even when popped as described above, a blister can become infected, Staph aureus infections being most common.  Blisters that have become infected can be treated with antibiotics prescribed by your GP. Blisters caused by a medical condition are treated by treating the underlying condition.

# Related Chapters
- Dracunculiasis
- Herpangina
- Herpes zoster
- Ulcer