From the symptoms they looks like heat
rash or sweat dermatitis. Prickly heat
(miliaria) is an itchy skin rash caused by trapped sweat. It tends to occur on
areas of the body where skin touches skin, such as under the breasts, on
the inner thighs, and under the arms. Tiny red spots with itching and pricking sensation
are the characteristic appearance of this rash.
Avoid using any lotion
s and creams for the meantime. use a mild cleanser with moisturizing properties like Cetaphil.