Melatonin is normally produced in our own bodies, in the pineal gland. It is also available as a supplement. It’s the brain’s way of signaling to itself — and the rest of the body — that it’s time to sleep.
There are a lot of products out there claiming (or at least strongly implying) that they’re going to make you a whole lot prettier. When it comes to hair and nails at least, there are two that actually work.