A rash below the breasts is a very all-purpose problem. It is generally a form of nuisance dermatitis and is called intertrigo exemplify by irritation of skin folds.
The most ordinary causes of breast rashes are extreme sweating, heat, lack of air flow, and wearing an ill-fitting bra that rubs alongside the breasts. Thus, feature like hot, humid climate and fatness contribute to this problem. Have a look at this below.