Hacker News Reader

Comment by abainbridge | Hacker News Reader

> administering melatonin prior to exposure to UV radiation increases cell survival and reduces oxidative damage. Topical melatonin applied to skin 15 minutes prior to exposure to UV radiation completely prevented skin redness (erythema) in a small randomized double-blind study of human subjects

This isn't necessarily good news. Sun burn is your body's way of reducing skin cancer. When your body detects too much exposure to sun, it kills the cells that are most likely to have suffered DNA damage. The soreness and inflammation are a result of that mechanism. Disabling that mechanism would cause skin cancer.

But maybe melatonin promotes DNA repair and thus the cells don't need to be killed. More research needed :-)

View on HN

Are you saying this as a medical research professional or just spitballing? Because the article send to be straightforwardly claiming that melatonin is reducing oxidative damage, not just disabling the visible effects. One of the referenced sources is entitled, "Melatonin as a major skin protectant: from free radical scavenging to DNA damage repair," which seems to be saying that the "more research needed" has already been done, like 10 years ago.

Guilty as charged. I didn't read the references. Thanks for the kick in the ass.

Free radical damage is not the main mechanism of UV-induced DNA damage. The main mechanism is direct dimerization as the photo-excited electron relaxes.

https://en.wikipedia.org/wiki/Direct_DNA_damage

It's hard to see how anything could prevent that other than sunscreen.

Think back to your high-school bio and chem; remember the whole idea of unpaired atoms or groups if atoms running around? That's a free radical. Remember that it takes energy to break chemical bonds? That's what UV does: provides the energy. The damage it causes is basically knocking random compounds and proteins apart. This leaves a random atom running around without an electron: a "free radical". Antioxidants donate an electron, thereby neutralizing the free radical. The real problem is when it does it to DNA; it can forcibly bond with it, and that's when you can get cancer. Which is why antioxidants are important.

Sunscreen turns UV light into heat topically, before it enters your cells.

Melanin, the body’s main pigment, turns UV light into heat inside the cells, but outside the nucleus. (The melanin is gathered into a shield-like collection of “melanosomes” which is “above” the nucleus relative to the outside of the body—like this: https://skincancer909.com/wp-content/uploads/2017/03/4K-sunh...) This has the same effect: the UV light never hits the DNA, and so never causes DNA damage.

Melatonin is known to recruit, or cause the production of, melanin within melanosomes. I’m not sure if this is the dynamic being discussed by the paper, though, or whether melatonin is more directly able to act in a similar capacity to melatonin exogenously. If it can, then the same explanation applies. (Does anyone know if pure melatonin powder looks black under a UV filter? That’d suggest it could act directly like melanin, despite its dissimilar chemical structure.)

This is what worries me about sunscreen. This is an entirely non scientific concern, but sunscreen is as much of a business as antiperspirant and shampoo, and both of those things disrupt normal endocrine rhythm, by definition.

Like even if the mechanism of action is perfectly sound, how does your body adjust with that over many years?

Reply on news.ycombinator.com