Inflammatory conditions of the skin may accompany contagious diseases or be due to an internal reaction. A list of other symptoms, the area of the body where the rash started, as well as a history of new medications, vaccines, or recent travel may all be important clues in determining the cause of a red blotchy rash.
Erythema Multiforme
Allergic reactions most likely to cause a red blotchy rash involve common medicines: antibiotics such as penicillin, sulfa drugs used to treat urinary tract infections, anti-psychotic drugs for schizophrenia, certain anti-convulsant medications and non-steroidal anti-inflammatory pain medicines such as ibuprofen or naproxen. Erythema multiforme (EM) may begin as pink bumps, developing into red round blotches, sometimes with a distinct center. The offending drug must be discontinued.
EM may also erupt from hypersensitivity to an infection or vaccine. According to an article published in the December 2006 issue of "American Family Physician" by researchers at Drexel University College of Medicine in Philadelphia, Pennsylvania, the herpe simplex virus (HSV), accounts for approximately half of EM cases, usually occuring in adults between the ages of 20 and 40. Children more commonly acquire EM as a result of a reaction to mycoplasma pneumoniaea, a fungal organism. Treatment of the primary infection resolves this type of skin condition.
Measles
The New Zealand Dermatological Society states that between 3 to 7 days after the onset of illness, the characteristic red blotchy rash of measles appears on the skin. Initial symptoms include fever, cough, sore red eyes and white spots in the mouth. Spread easily by droplets in the air or on surfaces, measles are contagious from two days prior to the onset of symptoms until five days after the rash appears. In the United States and many other countries, children are vaccinated against measles, preventing complications such as dehydration from diarrhea, deafness, pneumonia and death that the New Zealand Dermatological Society reports may occur in as many as 30 percent of measles cases.
Rocky Mountain Spotted Fever
An infectious disease transmitted by bacteria-carrying ticks, Rocky Mountain spotted fever is named after the area where it was first identified. Insects common to the Western, Eastern, and Southern United States and Central and South America carry the disease. According to the Mayo Clinic, the onset of symptoms such as high fever, vomiting, and sensitivity to light may occur up to two weeks after tick exposure, followed by a red blotchy rash that starts on the wrists or ankles and spreads to the palms of the hands, soles of the feet, up the arms and legs to the trunk. Prompt treatment with antibiotics can prevent life-threatening illness. Infections occur more commonly in warm weather, when skin and pets should be examined often. Ticks should be removed carefully with tweezers and preserved in a freezer bag for two weeks. In case illness develops, the tick can be tested for Rocky Mountain Spotted Fever. The disease is spread only through ticks and cannot be transmitted directly from person to person.
