The papule is usually defined as a small palpable lesion, not exceeding 10 mm, with non-fluid content (Fig. 4.1). In the USA and the UK, the maximum width of a papule is restricted to 5 mm in many textbooks. Lesions are generally elevated, above the level of the adjacent skin. Seen from above, a papule may be round (Fig. 4.2), oval, umbilicated (with a small central depression) (Fig. 4.3), or polygonal. Seen in profile, it can be flat, domed, sessile, pedunculated, or acuminate (conical, pointed) (Fig. 4.4). The surface may be either smooth (Fig. 4.5), eroded, ulcerated, or necrotic (Fig. 4.6), covered with scales (Fig. 4.6), crusts, or scaly crusts (Fig. 4.6); hair follicles may be prominent and confer a “peau d’orange” (orange peel) appearance (Fig. 4.7). Finally the distribution pattern may or may not be follicular (Fig. 4.4).

The consistency of a papule varies depending on its nature; some lesions are very hard, others soft and depressible (Fig. 4.8). Papules that result from epidermal proliferation or deposits (e.g., plane wart, seborrheic keratosis) usually have clear-cut and rectilinear boundaries and are often rough (Fig. 4.9), whereas dermal papules (e.g., ­granuloma annulare) are smoother and borders are less defined (Fig. 4.10). Papules must be distinguished from other palpable lesions which can be larger (plaques, nodules, tumors), fluid-filled (vesicles, bullae), or mainly due to alteration of the lesion’s surface (cutaneous horn, keratosis), which are also called keratotic papules.

The term tuber should not be used. It is a palpable intradermal lesion, either flat or barely elevated. Therefore, it is merely an intradermal papule (Fig. 4.11). These lesions often become chronic or tend to leave a scar on regression (e.g., lupus vulgaris). They are circumscribed and movable, ­relatively to the hypodermis.