A white hair grew on the right eyebrow and fell off.
It may be caused by malnutrition of individual hair follicles or abnormal melanin in hair follicles. Try not to stay up late often, which can also happen if you are overworked. I suggest you have a normal work and rest, ensure adequate sleep, eat reasonably, strengthen nutrition, and often participate in some outdoor sports and fitness activities to exercise and strengthen your physique.