ZocdocAnswersWhy do I get this big bump/rash thing on my legs and arms when I scratch them?

Question

Why do I get this big bump/rash thing on my legs and arms when I scratch them?

This is really odd i get this type of rash on me everytime i scratch.... but only if i scratch them. There will be nothing there and then all of a sudden it appears out of no where ... what is this???? theres a Guy at my work that has Mersa and I tend to think somthimes that this is what is it but im hoping not. do you have any idea what this could be????

Answer

It sounds like you probably have a condition that is known as "dermatographism." Essentially what this is a predisposition of the skin to develop inflamed red marks when it is stimulated by scratching. What happens is that scratching stimulates certain inflammatory cells in the skin, call mast cells, to release chemicals that cause local redness and inflammation. Generally speaking, this condition is very benign and, in fact, it is extremely common. It does not usually require any treatment, other than trying as best you can to avoid scratching the skin and causing the red welts to appear. Sometimes, however, dermatographism can be associated with more serious allergic problems. For example, if you notice that you are routinely breaking out in red welts all over your body, even without scratching, then this is something that will need to be investigated. Also, if you have any other allergy symptoms, such as swelling of the face or wheezing, then this is more serious. What I would recommend is that you set up a visit with your primary care doctor. They can perform a physical examination and make a diagnosis of dermatographism. They can also make sure there is nothing else going on that would require more extensive evaluation or treatment.

This answer is for general informational purposes only and is not a substitute for professional medical advice.

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