A bulla is a blister larger than 5 mm that can appear for several causes. Bullae are filled with liquid, have a raised profile and sometimes itch or hurt. Among the most common causes are contact with toxic compounds, infections, immune reactions or some diseases. Bullae can emerge as an allergic reaction to plants like poison ivy, sumac or oak. The exact cause can be determined by doctors by tests that identify immune proteins or after performing a biopsy, which involves cutting a small part of the blister in order to examine it under a microscope.

There are two main types of bullae. The tense types are located in the deep skin layers and don't break easily. The flaccid ones emerge on the skin surface and are very fragile, with a high chance of rupture.

In medical terms, bullae are large-size blisters with thin walls and a content of fluid. According to the definition, the fluid must be clear and the blister walls have to be transparent. There are several varieties of fluids: serum, lymph, blood or pus. Bullas are normally located on skin but they can emerge in other places. Such unusual locations are inner membranes in the nose, throat, mouth or lungs, as well as the eye corneas. The most common causes for a bulla are the herpes virus, burns, insect stings or skin allergies. Blisters should be shielded from exposure with a bandage and treated with dedicated lotions or creams.

The term bulla comes from a Latin word that means bubble or knob. It is used in the medical language to designate round shaped blisters that can be empty or filled with fluids. However, only the ones larger than half a centimeter in diameter are called bullae, while the smaller ones are named vesicles. The ones that develop on the membranes inside the lungs have a specific name and are known as blebs.

Common causes of bullae are skin injuries due to friction, frostbite, severe sun damage or burns of a chemical nature. Blisters are also caused by the herpes simplex virus, in which case they are known as cold sores. A number of plants and animals can cause blisters on contact, due to various toxic compounds. Some of the most common are the toxic plant poison ivy and many species of jellyfish. Bullae can also be caused by other diseases, which can be very serious conditions such as thyroid disease, chicken pox or autoimmune problems like lupus.

Blisters can be of two types. The epidermal ones form between the skin layers, while the subepidermal are located under the skin. The exterior layer of the skin is named the epidermis and epidermal blisters emerge when fluid accumulates in a space developed between two of its sub-layers. In the second case, the liquid fills the space between the epidermis and the next layer, called the subepidermis.

Treatment options

Bullae treatment has two separate objectives: to heal the root cause of the blisters and to cure the blisters themselves, as well as their side effects like itching. Topical corticosteroids are effective against the symptoms and can heal the cause as well, if it is immune related. If the bullae are caused by an infection or later become infested with pathogens, antibiotics can be prescribed. These can be taken orally or applied externally on the affected area. Severe blisters, like the ones that get infected, can leave permanent indentations or other scars on the skin.

It is a bad idea to break a blister and remove the thin walls that cover it. This can cause pain and serious infections. The blister should be protected with a bandage or patch and treated with external antibiotic or antiseptic creams. Another effective treatment is any product based on benzoin tincture. There are also a number of effective home remedies, such as petroleum jelly, tea tree oil, lavender oil or aloe vera gel.

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