If you’ve notice some different colored hairs in your beard—most often red—you’re not a medical anomaly. In fact, it’s quite common for body hair to take on different shades than the locks on your head. Although these differences might seem arbitrary, there’s science behind them.

The levels of pigmentation in your hair follicles ultimately determine your hair color. Each follicle contains a mixture of eumelanin (black or brown shades) or pheomelanin (red and yellow shades) pigment. Guys with low levels of brown eumelanin and high levels of yellow pheomelanin end up with blonde hair. Different combinations in each follicle yield different hair colors, which explains those random red hairs and dark patches.

Besides natural pigment, stress and malnutrition can change your hair color. Grey hairs are the first sign of stress, while dull, lackluster hair can point to a vitamin deficiency. But the biggest culprit of changing hair color, however, is the sun. Overexposure may lighten your hair, but it will weaken it in the process. Add a leave-in conditioner with SPF—like this one from NIOS Shield—after your shower to maintain your hair’s strength and color.