X-linked ichthyosis is considered one of the five main types of
ichthyosis (the others being lamellar ichthyosis, congenital
ichthyosiform erythroderma, ichthyosis vulgaris and
epidermolytic ichthyosis (formerly epidermolytic
hyperkeratosis)). X-linked ichthyosis is less common (occurring
in approximately 1 in 6,000 births), can range from mild to
severe, and occurs only in males. In X-linked ichthyosis, the
skin cells are produced at a normal rate but they do not
separate normally at the surface of the stratum corneum (the
outermost layer of the skin), and are not shed as quickly as
they should be. The result is a build-up of scales. The scales
of X-linked ichthyosis are often dark and usually cover only a
portion of the body. Typically, the face, scalp, palms of the
hands, and soles of the feet are free from scales, while the
back of the neck is almost always affected. X-linked ichthyosis
frequently improves in the summer. Babies with X-linked
ichthyosis often appear normal when they are born, but the skin