Petechiae and dermatitis are two common causes of red spots on the skin, say Mayo Clinic and WebMD. Petechia are small, often clustered red marks, says the Mayo Clinic. Dermatitis appears as a larger rash, reports WebMD.
Tiny red spots of petechiae result when capillaries, very small blood vessels, burst or leak into surrounding tissue, according to Mayo Clinic. Long periods of strain, such as from coughing, vomiting or crying, sometimes cause petechiae to appear on the face. Medicines like anticoagulants, atropine, naproxen and penicillin are other potential causes of petechiae. In some cases petechiae are a symptom of a more serious disease, such as hantavirus, Rocky Mountain spotted fever, leukemia or even scurvy. Finally, petechiae can be the result of injuries such as hard blows or severe sunburn.
Dermatitis is red inflammation of the skin, usually due to an allergic reaction, reports WebMD. Poison ivy, hair dye and rubber are common causes of contact dermatitis. Nummular dermatitis, characterized by round, red spots, is the result of factors like a hot, dry climate or excessively hot water in the shower. Some dermatitis, like eczema, is at least partially genetic, but it might be triggered by allergies.
Red spots on the skin often require very simple treatment, reports WebMD. However, any unusual or sudden discoloration should be discussed with a doctor to rule out underlying, serious conditions, says Mayo Clinic.