Hair loss occurs when you shed more than you grow back. Most people with male pattern baldness shed a normal amount of hair, but the hair in the male pattern baldness zone doesn't grow back after it's shed = hair loss. A normal person without male pattern baldness sheds up to 150 hairs a day but it does not mean their hair will get thinner because the hair grows back in. Something called Telogen Effluvium exists though, where the hair sheds so much and so fast that the regrowth doesn't have time to catch up, so the hair gets visibly thinner. This condition is temporary though, and usually lasts no longer than 6 months before it stops and the hair fills back in. Hope this helped.