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(flat 10 mm), nodules (solid lesion 0.5 to cm), pustules (elevation with pus), abscesses (elevated lesion >10 mm with purulent material), wheals (elevated lesion with local transient edema), vesicles (elevated lesion 10 mm containing fluid) Secondary descriptors include crust, scale, fissuring, erosions, ulceration, umbilication, excoriation, atrophy, lichenification, and scar In addition to these descriptions, it is also important to understand the distribution of the rash or lesion Distribution characteristics include localized, blaschkoid (following lines of embryologic development), widespread or generalized, and photodistributed (predilection for sun-exposed areas) Characterizing a rash or lesion using these descriptors narrows the differential diagnosis significantly The following sections of this chapter will divide skin changes by their primary descriptor and then will provide a framework for adding secondary characteristics to improve diagnosis PAPULES Papules can be quite varied and the following algorithm is used to help practitioners distinguish between some common papular lesions ( Fig 88.1 ) Papules With a Characteristic Appearance Many conditions can be diagnosed on sight For example, the experienced eye can easily distinguish milia from molluscum contagiosum (MC) and warts from the uncommon xanthoma Several clues make the process of separating these entities from one another easier such as color, distribution, and patient characteristics Milia Milia are 1- to 2-mm firm, white papules They are produced by retention of keratinous and sebaceous material in follicular openings Newborns often have milia on their face They frequently disappear by the age of month Milia can also arise from skin trauma, and can be seen in scars after burns and in healed wounds in patients with blistering disorders like epidermolysis bullosa Persistent milia may be a manifestation of the oral–facial–digital syndrome, hereditary hypotrichosis (Marie Unna type), and certain rare ectodermal dysplasias Because lesions that are not associated with syndromes often disappear spontaneously, reassurance is generally warranted, though lesions may be easily removed by carefully nicking the surface and expressing the keratin This can be a simultaneously diagnostic and therapeutic procedure Molluscum Contagiosum