When the body doesn't have enough vitamin A to work properly.

The body needs vitamin A for many basic functions, especially sight. If a person takes in too little vitamin A from plant or animal sources, some parts of the body may not work properly.

Symptoms of vitamin A deficiency include a limited ability to see in low light, poor growth in children, changes in skin and other tissues, and more-frequent infections. Another symptom is getting sicker than what is typical from infections, especially measles or infections that cause loose stools.

Treatments may include supplements and diet changes.