Linear porokeratosis is a rare skin condition characterized by streaks of reddish-brown patches surrounded by a ridge-like border. The patches usually develop in infants or young children, but they sometimes develop in adults. Patches may be on one area of the body (localized) or on multiple areas (generalized). They usually develop in a pattern over the skin known as the "lines of Blaschko," and most commonly occur on the arms or trunk. Some people experience itching or pain where the patches occur.

Linear porokeratosis is thought be a form of disseminated superficial actinic porokeratosis (DSAP). Researchers think that people with linear porokeratosis may have one inheritedmutation in a gene that causes DSAP. It is thought that a second mutation in that gene is acquired (a somatic mutation), occurring in only some cell lines. This may cause the presence of streaks of patches, rather than more widespread patches.

Treatment options depend on each person's symptoms. There are no specific recommendations for treatment because no randomized clinical trials have been done. Options may include topical therapies, oral retinoids, cryotherapy, electrodessication, and surgery. Linear porokeratosis can progress to skin cancer (squamous cell and basal cell carcinoma), so sun protection and watching for changes within patches are recommended.

• Topical therapies such as 5-fluorouracil (5-FU), imiquimod, retinoids, and calcipotriol.
• Oral retinoids.
• Cryotherapy.
• Electrodessication.
• Surgical removal.

Linear porokeratosis can progress to skin cancer (squamous cell and basal cell carcinoma). If the purpose of treatment is to prevent its progression to cancer, surgical removal is typically recommended. Sun protection is also important to decrease the risk for cancer. Watching for changes within patches may help to detect cancer earlier.