This is a congenital skin lesion involving the overgrowth of the outer layer of the skin. It is in a linear or swirled pattern. The texture can be rough and is usually darker than the surrounding skin which looks normal. It is benign and is commonly present at birth, or develops in the first year of life.
Keratinocytic epidermal naevi are found on the trunk or limbs. They are brown flat or raised patches. They can become thicker as the patient gets older. They often follow the lines of Blaschko.
They usually stay the same size into adulthood and cause no problems at all. Laser treatment or surgical excision can be performed if required.
References
https://www.firstskinfoundation.org/types-of-ichthyosis/epidermal-nevus