What Causes Burning Rashes On The Legs After Touching Fig Tree Sap?

In June 2015 my husband came in contact with Fig tree sap and developed several very large, very painful blisters where the sap had come in contact with his skin (on his stomach area). Several hours later, red, itchy patches began popping up - first on his thighs, then spreading to his shins. Within a week, he had a painful, itchy, burning rash on his legs, buttocks, torso, and upper arms, in addition to the itchy red patches. He had to get steroid injections to quell the inflammation and itch, sat in Aveeno oatmeal bath 4 times a day, and was given prescription lotions and antihistamines. As of now, the general rash has mostly subsided, but the painful, itchy, burning red patches continue. He s been to 2 doctors and 2 dermatologists, and none seem to be able to diagnose it. He takes meds for diabetes, high blood pressure, and high cholesterol, plus vitamin K, vitamin B complex, and a multi-vitamin. He is absolutely MISERABLE! Can someone help?