An orangish, papillomatous congenital plaque in the scalp is most typical.

NEVUS SEBACEOUS

The nevus sebaceous (NS) is a congenital hamartoma of sebaceous glands found most commonly on the scalp and face.

If untreated, 20-30% will develop benign tumors, e.g., trichoblastoma, syringocystadenoma papilliferum, apocrine hidrocystoma. Most tumors occur in adults older than 40 years.
Virtually all cases of NS harbor activating or KRAS mutations, which represent a postzygotic mutation and genetic mosaicism.

Clinical

At birth, an orange, red, or yellow plaque is seen, usually on the scalp. Some lesions are linear. Over the ensuing months, with the reduction of maternal hormones, the lesion tends to flatten out. During puberty, under the influence of circulating hormones, the nevus sebaceous will typically thicken again and may resemble a mulberry.

Rarely, a widespread form is seen and is analogous to an epidermal nevus.

Nevus sebaceous on the shoulder of a 22-year-old patient that grew a warty bump. The entire lesion was excised and showed nevus sebaceous with seborrheic keratosis.

Nevus Sebaceous in the axilla.

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