Canthaxanthin is a naturally occurring carotenoid pigment. People use it mostly as a food coloring, where it appears as E161g. Some take it orally to darken their skin, but major health authorities like the FDA have not approved that use because of serious safety concerns.
The biggest known risk is canthaxanthin retinopathy. That happens when crystals of the pigment settle in the retina, which may harm vision or cause no symptoms at all. Other common side effects include orange-red skin and orange-red stool.
This pigment is not an essential nutrient. No established dietary health benefit exists for humans.