As with any new concerning medical symptom, you should make an appointment to see your primary care physician
, or in this case a dermatologist
to have this rash evaluated. The rash you are describing sounds like a very common condition known as intertrigo, which is a type of rash which often forms under arms, around the groin and along skin folds. However, rashes can be the first symptom of a more serious condition, such as a weakened immune system or systemic disease such as cancer or bacterial infection.
Intertrigo is a type of rash that often develops between skin folds or in other warm, moist areas such as the groin or armpit. This type of rash can appear bright red and have small, tender red bumps just as you describe. Intertrigo is often caused by fungus, specifically Candida which is a species of yeast, but they can also be caused by bacterial or viral infections, so consulting with your physician is going to be key in identifying the right type of treatment for this rash. If you develop fevers, sloughing of skin or lesions around your mucous membranes (mouth and eyes) you should call your doctor
right away or go to the emergency room as this can be a more serious, life-threatening type of rash.
Please get an opinion from a medical professional before attempting to treat yourself. Your doctor may prescribe topical ointments or powders to help you treat this rash. You should try to keep the area as clean and dry as possible. Shower regularly and dry the areas well before getting dressed. Your doctor may also prescribe you a topical powder which helps keep the area dry.