If you are sweating heavily, your sweat pores can become blocked causing millaria or prickly heat. These show up as very small red bumps usually on the neck, upper back, and chest, and especially on areas where clothing rubs on the skin. Unfortunately, this is a tough one to avoid if you are susceptible and run in the summer. Loose clothing or a different neck line may help. Applying aluminum chlorhydrate containing antiperspirants to the affected areas might also work to reduce the sweating. A cool shower immediately after exercise may also help. If it gets really bad, you may have to alternate outdoor and indoor air-conditioned exercise sessions.
If you cannot get the rash under control, see your personal physician who may recommend you make an appointment with a dermatologist.
