According to Robert MacNeal, M.D., Section of Dermatology at the Dartmouth Hitchcock Medical Center, "rash" is the word used to describe a temporary skin eruption. There are many different types of skin rashes, and most can be seen in several diseases. One way to identify skin rashes is to see how they are exhibited during infection by a specific disease.
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A malar rash is a rash that covers the bridge of your nose and some of your cheeks. This is why it also has the nickname of “butterfly rash.” This rash is very photosensitive, becoming a darker red in sunlight. It can be seen in an autoimmune disease called systemic lupus erythematosus (SLE), a disease that primarily affects women. It is also seen in arthritic diseases that have been caused by viruses.
At first, this rash is red and slightly raised. It will spread and then merge to form a blotchy, lacy pattern across the body. This type of rash can be seen in a disease called erythema infectiosum, which is caused by a virus called parvovirus B19. Usually affecting children, the rash on their cheeks gives this disease the nickname of “slapped cheek fever,” as children look like their cheeks have been slapped. The rash soon spreads across the body, assuming the blotchy, lacy pattern.
This rash can be smooth, slightly elevated or seem scaly, but it is always purplish in color. Seen in a disease called dermatomyositis, you will see it on your eyelids and over specific joints of your fingers. Other possible locations include your forehead, chest, back, forearms, elbows, lower legs and knees.
This is the name given to a rash that looks like the measles. This rash is red and flat, and it will merge in some areas of your body. A morbilliform rash can be seen in a disease called Kawasaki syndrome. Like erythema infectiosum, Kawasaki syndrome also affects children, but it is an inflammation that affects the child’s blood vessels. Besides Kawasaki, the morbilliform eruption can be seen in many viruses, in scarlet fever and in toxic shock syndrome.
A petechial rash will start out flat, become raised, and then develop little pinpoints of hemorrhage. This rash can be seen in Rocky Mountain spotted fever, a disease you will get if you are bitten by the Dermacentor tick that carries a bacterium called Rickettsia rickettsii. You will have a petechial rash that starts on your ankles and wrists but then spreads to your arms, legs and trunk, including your palms and soles. A petechial rash is also seen in meningitis, if you have platelet abnormalities or have a decreased number of platelets. But in these disorders, the rash will not cover your body in the same pattern as Rocky Mountain spotty fever.