This Publication Is Searchable The Merck Manual of Diagnosis and Therapy Section 10. Dermatologic Disorders Chapter 109. Scales are heaped-up particles of horny epithelium. The most common scaling rashes are from psoriasis, seborrheic dermatitis, superficial fungal infections, tinea versicolor, pityriasis rosea, and chronic dermatitis of any type. Crusting occurs in many inflammatory and infectious diseases.
Erosion is focal loss of part or all of the epidermis.
It often occurs with herpesviruses and pemphigus. Ulcers are focal loss of the epidermis and at least part of the dermis. When ulcers result from physical trauma or acute bacterial infection, the cause usually is apparent. Less obvious causes include chronic bacterial and fungal infections, various peripheral vascular diseases and neuropathies, systemic scleroderma, and tumors. Excoriation is a linear or hollowed-out crusted area caused by scratching, rubbing, or picking.