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The Most Common Skin Diseases

By Molly Jenkins, Ph.D. ; Updated August 14, 2017

With more than 3,000 known skin diseases, it is not surprising that skin disorders are one of the most frequent reasons people visit their doctor. The most common disorders include seborrheic skin conditions, infections, chronic inflammatory skin diseases and skin cancers. These differ in their impact, with some causing mild to no discomfort, while others require long-term management or are potentially life-threatening.

Seborrheic Disorders

At some point in their life, many people will develop seborrheic dermatitis, characterized by oily, red and scaly skin that can be itchy. This condition most commonly occurs on the scalp as cradle cap in infants or dandruff in older individuals. It frequently affects the face, chest and upper back as well. Seborrheic keratosis is a skin growth often appearing in older adults, which is scaly, light brown to black and slightly raised. Although benign, seborrheic keratosis sometimes looks like skin cancer.

Skin Infections

Although skin acts as a barrier against germs entering the body, bacterial, viral and fungal infections can occur in the skin itself. Impetigo is an infection caused by bacteria. It consists of red sores, blisters and crusting and is highly contagious. Herpes simplex virus 1 causes cold sores. Another frequent viral skin infection is warts, caused by the human papillomavirus. Fungal skin infections are also common conditions. Tinea pedis -- athlete’s foot -- and tinea corporis -- ringworm -- are examples of these infections.

Chronic Inflammatory Diseases

There are numerous chronic inflammatory diseases of the skin. Acne is the most common, affecting a large percentage of adolescents to some degree. According to “Inflammatory Skin Diseases,” acne continues into adulthood in 10 percent to 20 percent of individuals. Psoriasis, characterized by persistent patches of red, scaly skin, can occur at any age and may run in families. It often affects the nails and may also cause joint inflammation -- psoriatic arthritis.

Eczema is a group of disorders causing red, inflamed skin. Atopic eczema is a common form of eczema that is caused by allergies. It usually starts in early childhood and improves with age. Rosacea typically starts in middle age with reddening of the cheeks and forehead. It can eventually lead to thickening of the facial skin and a large red nose.

Skin Cancer and Actinic Keratoses

According to the February 2015 issue of the "American Journal of Preventive Medicine," nearly 5 million Americans are treated each year for skin cancer. Basal cell carcinoma is the most common but least serious type of skin cancer. Squamous cell carcinoma is less frequent but grows faster, causing large growths on the skin unless removed by surgery. The least common skin cancer, melanoma, is potentially life-threatening, especially if it is not treated in its early stages.

Actinic keratoses are common scaly growths appearing in areas of the skin damaged by sun exposure. They are often red or brown and feel rough. According to the American Academy of Dermatology, actinic keratoses are considered precancerous because a small percentage will develop into squamous cell carcinoma if left untreated.


As many skin conditions look similar, consult with your doctor to establish the correct diagnosis. Also see your doctor if you think you may have an actinic keratosis or if you have any mole or other skin growth that is growing, changing color or producing symptoms such as bleeding or itchiness.

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