Many chemotherapy medications can include side effects related to skin changes. It sounds like your husband's physician is treating the rash, but as you described it is not working.
I will offer a couple ideas and suggestions when talking to your husband's physician.
Has your husband changed brands with any of the following items- personal soaps, laundry products or lotions?
Did your husband's physician rule out hives or cellulitis?
Is your husband taking any other medications for the first time along with the chemotherapy treatment? ( if yes, ask what the side effects could be)
If your husband's treatments are ending soon, then perhaps the skin changes will also lessen once chemo has ended. If your husband is just beginning treatment, you may want to ask your husband's physician about a referral to a dermatologist.