Develop A Rash On Fore Arms, Wrists Large Area Of

Develop a rash on fore arms, wrists large area of chest and sternum and penis. Rash appears in form of some small blisters and red colour, very itchy and dry skin on both hands.
Had this for six weeks, getting worse.
I work in the building trade and last two jobs very dusty.
No change regards to toiletries and laundry.
Thanking you in advance
Colin