It won’t cause hair to grow on your palms, but playing by yourself might have it downsides.
Here’s a description of one case, that of a girl who refused to stop playing, even after she developed sores on her palms.
On investigation, the researchers diagnosed ‘idiopathic eccrine hidradenitis’, a skin disorder that generally causes red, sore lumps on the palms of the hands and soles of the feet. Idiopathic palmoplantar eccrine hidradenitis has been previously found on the soles of the feet in children taking part in heavy physical activity, such as jogging, and it is thought to be linked to intense sweating. For the disorder to only affect the hands is very unusual. Furthermore, the patient had not participated in any sport or physical exercise recently and she and her parents did not recall any recent trauma involving her hands.
via B.A.D.