Tag: Photosensitive dermatitis

First described in the 18th century, Casal's necklace, or Casal's collar, is a distinctive red and hyperpigmented rash around the neck, serving as a tell-tale sign of pellagra, a severe nutritional disorder. Historically, it was named after the Spanish physician Don Gaspar Casal, who first identified the syndrome among the poor population in Spain in 1735.

Affecting approximately 1 in 30,000 individuals, Hartnup disease is a rare genetic condition that can lead to pellagra-like symptoms. Unlike nutritional pellagra, this occurs not from a dietary lack of niacin but from an inability to properly process the amino acid tryptophan.