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From your history , you seem to be having a dry skin
with some allergic manifestations too. Dry skin ,if not taken care of can cause itching and pigmentation , the itching may go worse due to stress
and frequent scratching this being a vicious cycle . identify your skin type , if it is dry , moisturize your skin regularly , with a good cream which has vit E , every night before going to bed.
You also need to avoid oily diet , eat a lot of green leafy vegetables.Drink lot of fluids as in juices and water too , this helps for every skin type .In case you have allergies, identify the source and avoid the same in diet as well as externally .
The large bumps on your knees,etc may be again a reaction to an allergen or another cause , which has to be evaluated further .
Take care to use the right soap/body lotions and also avoid cosmetics whenever possible , use a face wash which is mild and avoid soaps on the face , frequent change of soaps too may cause reactions .
Wishing you good health