In medicine, the term lesion refers to any abnormality of tissue in the body. Lesions can occur in any area of the body consisting of soft tissue, but are most commonly found on the skin or in the mouth. There are many different circumstances that can induce the formation of lesions.

Lesions of the skin can be divided into two main categories: primary and secondary. Primary skin lesions involve a variation in color or texture of the affected skin. Many primary lesions, such as moles and birthmarks, are present at birth.

Primary skin lesions can also be acquired over time. Some primary skin lesions, such as acne or warts, are caused by disease. Other possible causes of skin lesions include allergic reactions, which may cause lesions such as hives, or environmental agents, which can cause sunburn, abrasions, or other changes in the skin.

Secondary skin lesions, on the other hand, are abnormalities in the skin that are the result of primary lesions. These changes may occur as a natural progression of the primary lesion, such as a scab that naturally forms on an abrasion. Secondary skin lesions may also be the result of a person manipulating a primary lesion, such as scarring that results from an individual picking as his or her lesions.

While the vast majority of skin lesions are harmless, some can be an indicator of skin cancer. For this reason, it is important to keep an eye on moles and other changes in pigmentation of the skin. An asymmetrical or uneven border is one indication of cancerous lesions. Furthermore, lesions that are colors other than a uniform tan or brown or are larger than 5 mm in diameter should be examined by a physician.

Because lesions can be caused by a wide variety of agents, treatment varies depending on the cause. If lesions are the result of an infectious disease, physicians generally seek to treat the disease that is causing the lesions rather than the lesions themselves. Some topical antibiotics are also effective in preventing further infection. Other topical treatments, such as cortisol cream, can be applied to soothe itchy or irritated skin lesions. In many cases, treatment for harmless skin lesions is primarily cosmetic. For example, patients who are bothered by the appearance of a noncancerous lesion may resort to laser surgery in order to reduce the appearance of the abnormality.