Recurring Knee Rash

Hello, I hope someone can help me!
I have small red itchy bumps that appear on one knee and then transfer to the other.. they last about 2 weeks and then they go away completely.
Only to come back again a few weeks later.

This is the the third or fourth time they have appeared.

The bumps are very small, and only a few will appear at once.. But after a day or so more will appear until my whole knee is covered! But only on my knees, and at the beginning only one. Never anywhere else.

I don't think it is an allergy as they didn't go away (or even get better) when I went away to my boyfriends parents house. Also I washed the sheets in different detergent and there was no difference.

After two weeks or so they do disappear on there own, but a couple weeks later they reappear!
Since it doesn't seem to want to stay away permanently I'm getting pretty worried.
Please help!

[Dr_Aparna]

Hi,
Itchy bumps are usually due to an allergic reaction. It need not necessarily be only due to detergents, since there are so many triggers, some of which you may not be aware of.

The pathological reaction that takes place on your skin due to foreign particles is considered as allergy rash.
This kind of skin inflammation with swollen red itchy patches all over the body is the most common form of allergy rash.

In your case it could be from fabrics and clothing or any allergenic material (like creams or soaps) that your knee comes in contact with, which could be triggering it.
You can take anti-histamines like Cetrizine / Loratidine to treat it. Also you can apply Calamine lotion or Pramoxine lotion to help alleviate the itching.

ref:http://www.allergyasthmazone.com/allergy/factors-that-can-contribute-to-allergy-rash