Definition. Papules are pin-point to pea-sized, solid, circumscribed elevations of the skin, usually superficially seated.
They vary in size, shape and color and their diverse character and origin demonstrates that they are due to different pathological processes and are seated in different layers of the skin. In shape they may be rounded or angular at the base and more or less conical, flat or umbilicated at the apex. While papules never contain fluid they often develop into vesicles or pustules which dry into crusts or degenerate into ulcers, which in turn are followed by scars. In color they may be white as in milium; yellow as in xanthoma; bright red as in eczema; coppery red as in syphilis; violaceous as in lichen planus; or almost black as in some varieties of sarcoma. Papules may last for a long or short time, or even become permanent. They may be non-inflammatory as in keratosis pilaris or inflammatory as in eczema. They may be due to obstruction or obliteration of the ducts as in acne and milium; to new-growth infiltration as in xanthoma and lupus; to hypertrophy of the epidermic layer as in keratosis pilaris; or they may be due to hypertrophy of the papillary layer as in ichthyosis and warts. Thus it will be seen that the anatomical seat of papules varies. Papules which have been torn by scratching or rubbing present minute bleeding points or crusts at their apex. Besides the size, form, color and duration of papules, any concomitant conditions, if present, such as fever, itching or other subjective sensations, the extent of infiltration of adjacent skin and other lesions, should be carefully noted.
Various qualifying terms have been used in describing papules. Thus when the squamous feature is noticeable they are termed squamous papules and the eruption is known as papulosquamous. When vesicles or pustules are pre-eminent they are known as papulovesicles or papulopustules. The term lichen is erroneously used to describe a papular eruption as a whole. The same may be said of the term lichenoid which was formerly regarded as synonymous with the term papular. The French apply the term lichenification to a condition usually observed about the joints, characterized by thickening of the skin and aggregated papular elevations. Most authorities consider this a variation of chronic eczema or lichen planus.