Cause of Psoriasis on Arms

Psoriasis on the arms, like other forms of psoriasis, is caused by irregular immune function. In people with psoriasis, the immune system causes the cells that affect skin and nails to behave abnormally.5 These cells grow faster and are replaced more quickly than they are in people without psoriasis, resulting in symptoms like inflammation and plaques.6

Psoriatic bumps on the elbows happen because elbows are extensor surfaces—areas of skin covering a joint. Extensor surfaces are more likely to have psoriasis than skin areas not around a joint, although it is not known why.7 One theory is that the skin in these areas is under a lot of strain as the joints stretch, move, and are leaned on.