There are at least two common skin conditions that could give this set of symptoms.
The first, and the most likely, is a fungal or yeast infection of the skin. This is very common in the area between and under the breasts, occurring because fungus thrive in moist, dark, warm environments, such as the skin in this area of the body.
The second, and also common, is eczema
, which is an inflammatory condition of the skin which might be worsened by constant moisture from sweating.
Although both conditions can often seem similar in terms of symptoms to the average person, a doctor
can usually distinguish between the two easily just by looking at the rash. Telling the difference is important, because fungal infections are treated with anti fungal creams, whereas eczema is treated with a steroid cream. Applying a steroid cream to a fungal infection may make it worse.
Therefore, I would recommend making a quick appointment with your primary care doctor
. They should be able to take a look and tell you right away what is going on. Based on what they think, they can also prescribe the necessary medications for you to help clear this issue up as soon as possible.