The underwire bra is made to help women with large chests in a variety of ways, but there can be several significant problems. However, many of the issues faced are easily prevented or fixed.
The function of underwire bras is to create support for the breast tissue during the day. Underwires have traditionally been suggested for women with larger breasts who need more support, but underwire bras come in a variety of sizes and many women--both large and small breasted--use them.
Ill-fitting bras are the biggest problem that women face when dealing with underwire bras. In order for a bra to be comfortable, especially an underwire bra, the cup and band size must be correct. The bra can gape, painfully dig into the skin or cause chaffing if the fit isn't correct.
Women who are wearing a bra that is too big for them will find that gaping at the rib cage is a significant issue. Women wearing a bra that is too small for them in the cup will find that the underwire digs into their side painfully. Those wearing the wrong band size will likely experience chafing around the band or shoulders.
Underwire bras can sustain serious damage during washing and drying cycles. Washing underwire bras with other clothing means they are shuffled around too roughly, which can break down the elastic and fabric around the underwire. This will eventually cause the underwire to poke out from the sides or bottom of the bra. When the underwire is revealed, it can become painful and extremely uncomfortable to wear. Washing bras by hand and allowing them to air dry preserves the bra.
Underwire bras can easily bend and misshape the bra. The actual wire in most underwire bras is a thin-gauge metal strip. The metal is easily pliable, so when it's handled roughly the wire can bend in the center of the bra--creating an unflattering and uncomfortable fit. Once the wire is bent, it can be bent back. However, it will never seem the same again. Bent underwire bras should be disposed of.
Underwire bras can be very painful for some women. The underwire can dig into the underside of the breast. Cheap underwire bras tend to have less padding around the wire and thus can dig into the skin badly. To prevent pain, it's best to invest in more expensive bras with greater padding around the metal wire. They'll last longer than cheaper bras and will reduce pain.
There is some evidence that suggests wearing underwire bras--especially underwire bras that fit poorly--can increase the risk of benign but painful tumors in the breast tissue. It is believed that underwire bras that fit poorly can constrict and damage the breast tissue over time, creating benign or fatty tumors.