Blisters are pockets of fluid trapped between layers of the skin. They usually contain serum produced by the body as a defense mechanism. There is a wide variety of known causes for stomach blisters, but some arise from indeterminate causes. They can develop as a result of irritation, infection, or allergies. Biting insects such as spiders can inject toxins that cause blisters too.

Stomach blisters can develop because of friction between folds of skin. Warm environments compound this form of skin irritation, as does obesity and tight-fitting clothes. Chemical irritants such as laundry detergents or solvents can cause blisters. Compounds present in newly purchased clothes, such as starch or sizing, may also irritate the skin.

Viral infections can cause blisters to develop on the stomach. The signature feature of chicken pox, a viral infection most often affecting children, is itchy, red blisters. These blisters can develop anywhere on the body, including the stomach. The same virus causes shingles, but it only affects adults who have previously had the childhood version. Blisters from shingles usually develop on only one side of the body, with the blisters following nerve pathways.

Allergic contact dermatitis causes, among other symptoms, blisters at the point of allergen contact. Nickel is a common allergen, and belt buckles and zippers are often made of this metal. Contact of nickel items with the stomach can cause blisters in sensitive individuals. Different from allergic contact dermatitis is an allergic reaction, and blisters on the stomach can occur as a result of allergies to things such as latex, medication, or perfumes.

Miliaria, also called prickly heat, is a condition where the sweat glands become clogged and do not function properly. This causes small, water-filled blisters to develop on the skin of the stomach or elsewhere. Sometimes, bumps on the skin are not blisters but are actually a rash. A rash is a red, inflamed area of the skin with solid bumps. Scabies is a skin condition caused by contact with mites; the mites leave a rash as they burrow and infest the skin.

It can be difficult to pinpoint the cause of stomach blisters as they may not show up for days after exposure to the causative factor. Most stomach blisters are not cause for concern, but they may signal a more serious condition if they appear suddenly, appear in large quantities, or are accompanied by fever. Blisters filled with pus indicate an infection and require medical intervention.