Once your teen hits puberty, she will probably add "developing breasts" to the laundry list of changes that she is experiencing. She might even find that asking for a bra is pretty embarrassing, so it might be up to you, as the parent, to help her know when and how to buy a bra. By purchasing the right undergarment for the job, you make your teen's first bra shopping experience relaxed, comfortable and embarrassment-free.
Your teen might not need a bra for support, but because she wants a bra to fit in with her friends or to give her chest coverage under T-shirts and other clothes. A training bra is typically without underwires or padding, but is instead a comfortable cotton bra that gives your teen a little confidence while she is still developing. Look for a bra that is nonrestrictive and comfortable, which may have cups but may also be more like a sports bra. Your teen's peers might start wearing bras before she needs one, so keep the lines of communication open -- you may need to ask if your teen wants to go bra shopping or if she would like to try a training bra even if she does not need a ton of support.
Once your teen has experienced some degree of breast development, she will likely be ready to transition from a training bra to an everyday bra. An everyday bra should be one that is comfortable to wear, but may also have features like separate cups, underwires and even some light padding to give your teen's developing breasts some shape and coverage under her shirts. Your teen's everyday bra should help her feel covered, supported and confident, otherwise she might be less inclined to wear it regularly. While bras with colors and patterns are definitely fun for teens, your teen should still have a bra that is less likely to show through clothes -- in white or nude -- before buying bras that have more personality. That way, she always has the right undergarment for any outfit.
If your teen is active in sports or fitness, a sports bra is a must. Sports bras should fit snugly and give your teen plenty of support when she is being physical. For smaller breasts, a pullover, constrictive cloth bra is usually fine, but if your teen has bigger breasts, she may need a sports bra with adjustable closures and underwires or separate cups to offer the most support and coverage.
Lingerie and department stores usually offer free fitting services, where a trained professional can measure your teen and suggest the proper size. Your teen, however, might be too embarrassed to have a stranger measure her for the proper fit, so you can do the measuring at home before you go shopping to limit the blush factor. Use a tape measure and measure first your teen's ribcage, just under her breasts -- this is her band size. Then, measure the breasts directly across the nipple.
Once you have both measurements, subtract the band size from the bust size. If the bust size is up to half an inch larger than her band size, then your teen's cup size is AA. If the difference is half to one inch larger, your daughter is an A-cup. A one to two-inch difference is a B-cup, a two to three-inch difference constitutes a C-cup, while a three to four- inch difference is a D-cup and a four to five-inch difference is a DD or E cup. Once you have the band size and the cup size, you can shop for your teen's first bra according to her needs.