Popular science [Shaping underwear can treat side breasts? It didn’t work! Long breasts, fundamentally, are due to the incomplete degeneration of our physiological structure, which is a congenital breast abnormality (which can occur in both men and women). In addition, the raised flesh under the armpits may also be fat. But regardless of whether the armpit is a side breast or a fat meat, wearing shaping underwear can only temporarily wrap the excess meat in, and the meat runs out again with a little movement. And too tight underwear will compress the armpits, making the breast lymphatic return poor or compressing the brachial plexus, causing breast swelling and arm numbness. (via BTV, I am a big doctor official micro)
Source: Guangdong 12320