“I’ve noticed that in autumn some thin grey hair appears on my head. I usually pull it out. I read somewhere not so long ago that if you pull out a grey hair, 3-4 more grey hairs soon appear on its place.”
Every hair grows from one hair follicle, i.e. a hair follicle can produce only one hair. Therefore, if you pull out a hair, it can’t be replaced by several hairs but one. Sometimes a pigmented (not gray) hair can start to grow from the same follicle. But still you shouldn’t pull out your gray hair, because it quite often leads to serious consequences. You can damage gentle follicles of the scalp and it can result in some infection. To say nothing of hair loss. It’s much safer to to take advantage of tonic shampoo, henna, hair-dye or harmless hair color. Or you can just leave everything as it is. Please believe that having gray hair doesn’t make you a hoary antiquity. And it’s much better to have healthy gray hair than full-colored but poor.