Gray hair can occasionally be an indication of sickness, such as thyroid disease or alopecia areata (a common autoimmune disorder). Inform your healthcare physician if you see any additional tell-tale indicators, such as balding patches. However, don't be alarmed; they are uncommon and pose minimal risk. Generally speaking, gray hair is a sign of good health. It may indicate that you have more antioxidants in your system to prevent DNA damage that can lead to gray hair. Or it may be because you're using up some of your melanin reserves. There are several conditions that can cause gray hair, including iron deficiency anemia, vitamin B12 deficiency, hyperthyroidism, Cushing's syndrome, and lithium use. If you have gray hair, make sure to get checked by a doctor so you can figure out what the cause is.