Stress causes the constriction of capillaries which feed the hair follicles. When this happens, the amount of oxygen and nutrients nourishing the blood capillaries is considerably reduced. Stress causes excessive sweating. Abundant perspiration attracts airborne debris and pollutants that clog the hair follicles. Stress also affects the arrector pili muscles which get contracted by cold stress and emotional stress, causing decreased blood flow to the scalp and consequently hair loss.
Physical activity reduces stress and increases the blood flow to the extremities, including the head and scalp. Regular yogic exercises, especially Pranayama would help alleviate stress promoting overall general well-being and hence healthy hair. We call all this Hairobercise!