I have small bumps on butt,knees,elbows..can anyone help about the problem
It's hard to suggest anything without seeing pics. This should help you add images:
https://patient.uservoice.com/knowledgebase/articles/402861-how-do-i-add-an-image-to-my-post
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They may be different in type but probably all are cause by pressure . ie sitting on butt, kneeling on knees and resting on elbows. Do the butt ones ever get infected?. difficult to know exactly what we are talking about without pics. Can I ask how old you are?