Hypohidrotic ectodermal dysplasia (HED) is a genetic disorder of ectoderm development characterized by malformation of ectodermal structures such as skin, hair, teeth and sweat glands. It comprises three clinically almost indistinguishable subtypes with impaired sweating as the key symptom: Christ-Siemens-Touraine (CST) syndrome (X-linked), autosomal recessive (AR), and autosomal dominant (AD) HED, as well as a fourth rare subtype with immunodeficiency as the key symptom (HED with immunodeficiency) (see these terms).

Dryness of the eye related to deficiency of the tear film components (aqueous, mucin, or lipid), lid surface abnormalities, or epithelial abnormalities. Keratoconjunctivitis sicca often results in a scratchy or sandy sensation (foreign body sensation) in the eyes, and may also be associated with itching, inability to produce tears, photosensitivity, redness, pain, and difficulty in moving the eyelids.