It is difficult to clearly state that stress causes gray hair because, stress itself can have many adverse health effects, like heart problems, stomach or digestive disorders, sleeping disorders and a poor immunity. It can also cause breakouts in skin in the form of acne, and psoriasis. All of these health disorders can cause your hair to fall and turn them gray. So, not directly but indirectly in the form of a domino effect (a chain affect), stress can stimulate gray hair and hair loss.