Generally we lose between twenty-five and a hundred and twenty-five hairs per day. Most of the time, new hairs grow from the old follicles. For some reason that’s not entirely understood, men tend to go bald on the tops and fronts of their heads. Actually, the hair doesn’t go away completely; it just becomes arrested in the early, peach-fuzz stage. So as full-length hairs fall out naturally, the follicle produces only a tiny replacement that will never grow to full size. Women don’t tend to go bald, but as they get older, their hair gets thinner by the same process. Of course, if you’re losing a lot of hair in a short time, you may have a scalp problem and should probably see a doctor, but a few hairs in the bathtub shouldn’t raise any alarms.