By Gary M. White, MD

Flat warts

Flat warts (FW) represent a superficial infection of the skin by human papillomavirus (HPV). It is common in children and on the legs of women who shave. See also Warts.


Multiple flat-topped, flesh-colored papules are typical. Their distribution is grouped and assymetric, helping to distinguish them from seborrheic keratosis in the adult. FWs tend to occur on sun-exposed skin, e.g. the dorsa of the hands or the forehead. It appears the immune suppressive nature of sunlight predisposes to flat wart infection.

Shaving the legs or beard area can cause multiple lesions through auto-innoculation. Linear FWs are common. In some cases, the lesions are brown and resemble nevi.


Liquid nitrogen therapy every 1-3 weeks may be performed until all lesions have resolved. If on the legs, cessation of shaving is preferred. If in a sun-exposed area, sun protection is desirable, as it may be that UV suppresses the immune system and prolongs the condition. Topical imiquimod nightly may be tried.

Topical imiquimod every other night alternating with a topical retinoid (e.g., tretinoin) the other nights may be beneficial. Other therapies that have been tried include 5-FU 5% topically BID for 2-3 weeks. The patient must be informed of all the typical side effects. Topical imiquimod 3/week completely cleared the recalcitrant, facial, flat warts after 3 weeks in a 21-year-old woman.

Topical immunotherapy with diphenylcyclopropenone was successfully used in one case [Eur J Derm 1998;8;488].

Lidocaine followed by light curettage is appropriate and effective in older patients (not young children who don't like needles), and when the warts are fewer in number. Treatment every 3-4 weeks until gone may be done.

The YAG laser has been employed successfully for flat warts. PDL is commonly used and 10% ALA is particularly beneficial [JEADV 2016;30;1700]. The pulsed dye laser was used to treat recalcitrant flat, common, plantar/palmar and periungual warts in one study [Cutis 1995;56;230]. Flat warts were most responsive.

Oral isotretinoin 30 mg/day for 12 weeks cleared all 16 patients (15 placebo) in a randomized, blinded study [J Dermatol Treatment 2015;26;78-82].

Additional Pictures

Flat warts Flat warts

Koebnerization of flat warts. The virus is spread in a line by scratching.
Koebnerization of flat warts

Flat warts resembling moles on the cheek of a child.
Flat warts on the cheek mimicking benign nevi


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