There are many possible causes for what you are describing and a definite diagnosis cannot be given without a physical examination. Therefore, it is important to make an appointment with your primary care provider or dermatologist
(skin specialist) to have a thorough discussion and examination of your rash. However, there are a few conditions that are common that I will discuss here. The first is called keratosis pilaris. It affects as many as 40% of the population and is more common in women. It causes red small rough bumps on the backs of the arms, thighs, buttocks, etc. It is usually more pronounced during the winter months. It is completely harmless and usually gets better with age. Another potential cause of your symptoms is eczema, a genetic skin condition characterized by dry, red, itchy patches on the skin. It can range from mild to severe and can be associated with allergies and asthma
. Another possibility is allergic dermatitis, meaning that your skin is reacting to something, such as your clothes or soap, and is causing the rash.
In the meantime, until you see a doctor
to get a definitive diagnosis, keep your skin clean and well moisturized.