Bones, undercaps, headbands.. whatever you want to call them, they do the same thing and that is slowly and mercilessly thin your hairline. I know that I have done a post on them before (paradoxically, I was saying how versatile and useful they are), but I highly recommend that you do not regularly wear them especially if you are noticing your hair is getting thinner at the front.
Here are some simple tips to prevent your hair from thinning:
1. Scrunchies are a lot gentler on your hair than elastic hair bands. Yes, they are those ugly things from the 1980's but they don't pull on your hair as much because they are made from fabric. I think the best scrunchies to go for are those big, vile velvety ones.. Don't make that face.. No one's going to see!
2. Don't tie your ponytail back too high
3. Never tie the front parts of your hair (i.e. fringe) back with the rest of the ponytail: this will thin your hairline before you know it. Always leave the fringe part untied and..
4. ..pin your fringe with hair pins to the sides of your head. This means there is no weight on those hairs and also means that you don't have to wear an undercap to prevent hair from peaking through.
5. Don't tie the ponytail or headscarf too tightly
6. Not that I think most of you would like to wear them anyway, but I would recommend steering well clear of two-piece hijabs like the Al-Amiras.
(The top photo was taken from yesstyle.com)