What is this rash ?

Last night my mother noticed she had this rash on her arm, the bumps were a little bit more swollen and they itched a little, she also said that they looked like white heads before she scratched them.

I would've thought they were just pimples or something but the formation of them and the redness around them makes me think it could be something else. Does anyone have a clue ? All help would be much appreciated!!