Even before they appeared in Vogue in 1907, according to Fashion Era, bras may have actually been worn in the Cretan times. Bras represented freedom from the restricting corsets of the Victorian era, but studies have shown that bras—padded ones included—may have some dangers associated with wearing them.
According to Doctors Singer and Grismaijer, because the bra is "an elastic garment designed to alter breast shape," the restriction placed on the breasts can prevent the lymphatic vessels from flushing out harmful substances in the breast tissue, causing them to toxify. With padded bras, this is all the more emphasized because the padding adds to the restriction, holding the breasts in an unnatural position.
By wearing a padded bra, you not only restrict the lymph glands, but also the lymph fluid. Restriction of this fluid can cause lumps in the breasts as well as fibrous tissue and cysts.
Wearing a padded bra can reduce melatonin in the body, thanks to its unnatural restriction. Melatonin regulates your sleep patterns, aging process and the function of your immune system, as well as slows breast cancer.
A padded bra can reduce the circulation in the breast tissue by pressing the breast against the chest. In extreme cases, the tissue can be separated from the main tissue of the breast inside the padded bra.