Question

I have been readingan articlediscussing a study by Tiffany Slater and Maria McNamara in which they identified molecular evidence of phaeomelanin in the fossil record. Slater is quoted as saying scientists still don’t know how – or why – phaeomelanin evolved because it is toxic to animals. I am curious what toxicity is being referred to here, since looking into it has only turned up the fact that phaeomelanin is responsible for red haired pigments in humans as well as reddish coloration in other animals, and the only mentions I've seen of toxicity are either phototoxicity that might occur when exposed to certain kinds of light, or increased susceptibility to skin damage from sunlight. I did find a few studies in the search results whose titles were completely impenetrable to a layman such as myself, so maybe there is more information there that I wasn't able to dig out. Is there a little more context around this statement that phaeomelanin is toxic that I am missing? I'm especially interested in information in layman's terms as I am not deeply familiar with the field of biology, but I am always curious.

Answer 1

Phaeomelanin is toxic in the context of its potential to cause cellular damage due to phototoxicity when exposed to UV light. While melanin, including phaeomelanin, has an essential role in protecting the skin and providing pigmentation, the red pigment can increase the risk of skin cancer. Balancing UV protection, vitamin D synthesis, and avoiding photodamage is crucial for skin health.

Step-by-step explanation:

Phaeomelanin and Its Toxicity

Phaeomelanin is one of the two primary forms of melanin, with the other being eumelanin. Phaeomelanin gives a red color to hair and skin pigmentation, while eumelanin is responsible for black and brown colours. The statement about phaeomelanin being toxic refers to the substance itself and the fact that it can generate reactive oxygen species when exposed to UV radiation. These reactive species can damage cells and are linked to an increased risk of skin cancer, particularly in individuals with fair skin who produce more phaeomelanin. This phototoxicity is what raises concerns about its toxic nature.

While phaeomelanin does play a role in providing colouration, its interaction with UV light presents a risk of cellular damage, making it potentially harmful or 'toxic.' On the other hand, melanin in general - including eumelanin - helps protect the skin by absorbing UV radiation. The balance of melanin types and levels in an individual is dependent on multiple factors, including genetics and exposure to sunlight, with implications for health pertaining to UV protection, vitamin D synthesis, and potential photodamage.

Conditions such as albinism result from a genetic deficiency in the enzymes responsible for melanin production, leading to a lack of pigmentation and an increased vulnerability to UV exposure. The role of melanin in skin health and adaptation is a complex interplay that reflects evolutionary responses to environmental pressures, such as levels of UV radiation.