In rats, vitamin A deficiency has severe effects on secretory epithelium. Columnar cells become squamous in type and keratinised. Dental development is severely affected and secretory cells of salivary glands also become squamous and keratinised. However, there is no evidence that vitamin A deficiency causes such changes in humans.

Successful treatment of keratotic plaques (leukoplakias) with retinoids (vitamin A derivatives) has been claimed but not confirmed. The toxic effects of these drugs are severe and they are teratogenic. Epidemiological studies have suggested an association between low vitamin A intake and oral and other cancers, but there is growing doubt whether beta-carotene is beneficial or harmful.

Riboflavin deficiency can occasionally result from a malabsorption syndrome. In severe cases, there is typically angular stomatitis, with painful red fissures at the angles of the mouth, and shiny redness of the mucous membranes. The tongue is commonly sore. A peculiar form of glossitis in which the tongue becomes magenta in colour and granular or pebbly in appearance, due to flattening and mushrooming of the papillae, may be seen but is uncommon. The gingivae are not affected. Resolution follows within days when ribo/>