Hi

I have dark black patches on my left arm which is itchy. After shower and after workout my skin in this area becomes more n more itchy.. My left arm has lost its normal colour and my right arm is cultivating the same symptoms. 

I consulted two well known dermatologist of my city and both said that its due to sunburn and gave me medicines which have not worked for me at all. 

Neither the itching stopped nor did my arms turned normal.

Even the back of ankle itch a lot and is turning black. 

Please give me some remedies and suggestions.