Thomas Jones, a boy with ichthyosis, a skin disease that resembles fish scales. Colored lithograph by J. Perry, 1841. Ichthyosis is a heterogeneous family of at least 28, generalized, mostly genetic skin disorders. All types of ichthyosis have dry, thickened, scaly or flaky skin. In many types there is cracked skin, which is said to resemble the scales on a fish; the word ichthyosis comes from the Ancient Greek meaning "fish."