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The trunk is a general term for the core body region including the chest, abdomen, flanks, and back. The trunk has many unique characteristics. In many people it is a site of minimal sunlight exposure as it is usually covered by clothing. Dermatoses within this distribution may be caused by an allergic contact dermatitis due to chemicals in clothing, soaps, dryer sheets, and other allergens. Since the trunk is generally covered by clothing, this occlusion often creates a warm, humid environment ideal for the development of diseases such as folliculitis, acne, and tinea versicolor. A high density of sebaceous glands in the presternal area may provide an ideal location for pityrosporum ovale yeast proliferation, making this a common location for seborrheic dermatitis. Skin folds, such as the abdominal skin folds and inframammary creases are prone to intertrigo and/or maceration, increasing the risk of developing cutaneous candida infections among other dermatoses. The trunk is the most common location for herpes zoster. The umbilicus is unique in that it has a high density of apocrine glands. Interestingly some conditions including psoriasis and scabies often favor this site.


Skin diseases primarily involving the trunk can be broadly categorized into inflammatory dermatoses, infections, and pilosebaceous diseases (see Table 34-1). The inflammatory diseases are the most common cause of skin disease on the trunk, however infectious skin diseases are more common in hot humid climates, in obese or immunocompromised patients. The trunk is the area of the body that is most involved in diseases such as morbilliform drug rashes, guttate psoriasis, tinea versicolor, and pityriasis rosea.

Table 34-1.Differential diagnosis for diseases of the trunk.

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