Ichthyosis is a family of genetic dermatological conditions seen in humans and domestic animals. The word comes from Greek ?????s?? lit. "forming fish", as people or animals with ichthyosis have scaly skin which can vaguely resemble the scales of a fish.

The term ichthyosis is sometimes used to refer to the specific condition ichthyosis vulgaris. Ichthyosis was formerly referred to as "pseudo-leprosy," as it can produce an appearance superficially similar to that of leprosy.

While ichthyosis acquisita is acquired (as its name indicates), most forms of ichthyosis are considered congenital. These types include:

Ichthyosis vulgaris
X-linked ichthyosis
Ichthyosis lamellaris
Epidermolytic hyperkeratosis
Harlequin type ichthyosis
Netherton's syndrome
Sjögren-Larsson syndrome

A physician (or veterinarian) often can diagnose ichthyosis by looking at the skin. A family history is also very useful. In some cases, a skin biopsy will be done to help to confirm the diagnosis. In a biopsy, a small piece of skin is removed and examined under a microscope. In rare instances, genetic testing may be helpful in making a diagnosis. Ichthyosis is not more or less common in any ethnic group. As of now, there is no way to prevent ichthyosis.

Treatments for ichthyosis often take the form of topical application of creams and emollient oils, in an attempt to hydrate the skin. Retinoids are also used for some conditions. Exposure to sunlight may improve or worsen the condition.

There can be ocular manifestations of ichthyosis, such as corneal and ocular surface diseases. Vascularizing keratitis, which is more commonly found in congenital keratitis-ichythosis-deafness (KID), may worsen with isotretinoin therapy. Ectropion, if it occurs, can be treated surgically after skin hydration.