Nobody likes to find their first gray hairs. Those hairs are a constant reminder that you’re getting older—but what if you’re not older when you start going gray? 
Although most people won’t see a significant number of gray hairs until they reach their 30s or 40s, some begin noticing a change much earlier. This isn’t indicative of your overall health, so it’s nothing to worry about. Still, if you’re looking to retain your hair color for as long as possible, it’s a distressing development. If you’ve ever wondered why you’re seeing the occasional white hair, we’ve got the answer. First, though, you’ll need to understand why hair changes color in the first place.
Hair coloration is caused by the presence of melanin (or lack thereof).
There are two types of melanin: light (pheomelanin) and dark (eumelanin). Your hair color is determined by how much of these melanins you have. 
Melanin production ramps up shortly after birth, which is why many Caucasian babies are born with blonde hair and blue eyes only to have their eye and hair colors change as they grow older. Cells called melanocytes create and control the melanin for each hair follicle. 
Melanocytes stop triggering pigmentation when your hair follicle is about to fall out, which naturally occurs every 100 days or so. As we age, our melanocytes become exhausted, and they’re eventually unable to function normally. That causes hair to lose its coloration and turn white or gray.
Several factors determine how long melanocytes last before they’re too exhausted to inject melanin.
The most important factor, of course, is genetics. If your parents dealt with graying hair at a young age, there’s a pretty decent chance that you’ll have the same experience. 
Hormones also play a role, so if you’re suddenly going gray, you may want to schedule a visit with a physician. This is especially important if you’re feeling fatigued or if you notice any other symptoms that could indicate a hormonal disorder. However, as dermatologist Laurence Meyer pointed out in a piece for Scientific American, graying hair usually isn’t a sign of any disease.
“Graying in a young adult is not itself a sign of any health problem,” Meyer writes.
Other factors that seem to be associated with melanin production include climate, chemical exposure, and nutrition. In one case, researchers successfully reversed premature graying by treating a patient’s vitamin B12 deficiency. 
If you’re going gray in your 20s, however, you probably won’t find such a simple solution. Most grayness seems to be caused by a single gene, according to a paper published in Nature Communications. The good news is that scientists are looking for ways to alter this gene to restore pigmentation. “We might have drugs that boost or stop the protein from acting and change the amount of melanin in hair follicles and change the hair internally,” said Kaustubh Adhikari, one of the authors of the study. “So once the hair comes out like the way you want, you don’t have go out and buy dyes.”
