Blisters are fluid-filled swellings that form within or just under your skin. The clear fluid in the blister is called serum. Serum is the fluid part of the blood that does not contain red blood cells and separates when the blood clots. Blisters occur when this fluid leaks into the skin, forming a raised bump just under the outer layer of skin (the epidermis).
If the skin is crushed, or very tightly pinched or squeezed, a blood blister may form. This happens when the impact on the skin is strong enough to cause a small blood vessel to rupture (break). Small blood vessels are located close to the surface of the skin, and a rupture allows blood to leak into the tear between the layers of skin.
Occasionally blisters become infected, and are filled with yellow pus.
Blisters are usually the result of heat injury, such as sunburn, or from repeated friction, such as shoes that rub. Any rubbing of the skin, if continued long enough, can cause blistering. Very short periods of intense rubbing of the skin will also cause a blister.
Blisters are common on the hands and feet, as these areas of the body often 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 blisters when it comes in contact with chemical substances or cosmetics. This is known as contact dermatitis.
There are also a number of medical conditions that cause blisters to appear on different parts of the body. This type of blister is usually filled with pus rather than clear fluid. The most common causes of skin blistering that are unrelated to heat or friction are:
a form of eczema causing itchy palms or soles of the feet (pompholyx), and
hives (angioneurotic oedema).
Other much rarer conditions that cause blistering include:
Pemphigus (a serious skin disease in which blisters rise on slight pressure and rupture easily, leaving raw areas that easily become infected);
Bullous pemphigoid (a skin disease in older people that features large, tense blisters);
Dermatitis herpetiformis (an uncommon skin disease causing intensely itchy red spots found symmetrically on the back and elbows);
Chronic bullous dermatosis of childhood (a disease featuring blisters on the skin, mouth, vulva and linings of the eyelids).
Blisters may be single or multiple. They occur when the skin rubs against another surface, causing friction, or when the skin is burnt. A tear occurs in the upper layer of skin, which forms a space between the layers. The surface of the skin remains intact and is pushed outwards as fluid from the blood seeps into the newly created space.
Blisters may be felt as a slightly bouncy swelling as the fluid pushes against the thin layer of skin. They may appear where you have felt rubbing against the skin, or where your skin has been burnt. Some blisters are painless, while some are tender to pressure.
Blood blisters are dark in appearance and are often more painful than normal blisters.
Infected blisters are filled with pus. There may also be redness around the blister, and the skin may feel hot and painful.
Blisters caused by friction and burning are usually obvious and the cause is usually clear. Blisters that appear without heat or friction can indicate an underlying condition. See your GP for diagnosis and to identify suitable treatment.
treatment. As new skin grows beneath the blister, the fluid contained within it is slowly absorbed, and the skin on top dries and peels off.
Try to keep blisters intact to avoid infection. Unbroken skin over a blister provides a natural barrier to infection. Never pierce the blister with a needle, but allow the blister to break on its own.
When the blister bursts, you may need to cover the area with a dry, sterile dressing to protect it from infection until it heals. Blood blisters should also be left to heal of their own accord. They are often painful, and you may wish to apply a cold pack straight after the injury. As with normal blisters, it is important to keep the area clean and dry, and protect it with a sterile bandage to prevent infection.
You should consult your GP if blisters become infected, recur frequently, form in unusual locations, or are very painful. Signs of infection include pus draining from the blister, very red or warm skin around the blister, and red streaks leading away from the blister. Your GP will usually prescribe antibiotics to clear up the infection.
You should also see your GP if the blisters are caused by contact with chemical substances.
Blisters on the feet can be prevented by wearing comfortable, well-fitting shoes. Footwear for long walks should be ‘broken in’. Socks should be washed and changed daily.
Wear work gloves for manual jobs such as gardening.
Use sunscreen and cover up during the hottest part of the day to avoid sunburn. Moisturising, after-sun or calamine lotions can help to ease the discomfort if you do get burnt. Other minor burns can be treated at home and usually do not need any dressings. Running the burn under cold water and taking painkillers such as paracetamol or ibuprofen can help.
source NHSDirect 151204