It is best to visit the dermatology department of a regular hospital when these bumps suddenly appear on the underside of the chest. There are many diseases that can cause similar symptoms to appear. The first is the occurrence of skin allergies, for example, sometimes due to the friction of clothing, or for some other reasons, some localized bumps can occur, accompanied by a significant itching sensation. The second reason why bumps appear under the chest may also be directly related to fungal infection. Then there are some patients who have small bumps under the chest that are prickly heat, which is more common in women. Because women sweat more under the chest and do not breathe easily, prickly heat can occur in this area, which can also be itchy or accompanied by tingling.