It must be kept in mind that lesions in skin disease may undergo a sequential evolution, resulting in a variety of identifiable changes in the skin, that when observed together can assist in deducing the underlying pathologic changes, and formulating a differential diagnosis. Color changes can be due to any number of causes, including erythema, hemorrhage, or pigment changes. Changes in pigment may be due to increases or decrease in normal pigmentation. Papule Papules are circumscribed, solid elevations of the skin, up to 1 cm in diameter. The elevation may be due to accumulation of cells, fluid, debris or metabolic deposits and may be follicular or interfollicular in orientation.
Papules often begin as erythematous macules.
Pustule Pustules are well circumscribed elevations of the superficial layers of the epidermis. Like papules, they may be follicular or interfollicular in distribution. It must be kept in mind that pustules, due to the thinness of the epidermis are usually transient. What is often observed is a transition from erythematous macules to papules to relatively few pustules to small crusts and scale . Vesicles A vesicle is a well demarcated elevation of the superficial layers of the skin less than 1 cm in diameter.