Husband has very red skin w/yellow blisters in his crotch and inside leg area. Temperature 99.9. Yesterday just looked like a heat rash w/itching and burning. Today seems much worse. The reddest I have ever seen

Need to see to ID. This rash would likely need to be examined and more history obtained to be able to provide you with useful input about the diagnosis or possible treatment.
This . This rash could be a few different things. - impetigo is a skin infection caused by bacteria - either streptococcus or staph. This needs to be treated with antibiotics. - contact dermatitis is skin inflammation. It can be caused by plants such as poison ivy or poison oak or it can be from contact of a chemical or item that a person is particularly sensitive to. This is usually treated with steroid creams or oral steroids. - viral illness such as chicken pox, shingles or herpes can also cause painful blisters on a red base. This can be treated with anti-virals or just needs to run its course depending on the severity of the infection. The best thing to do is to contact his doctor and have him seen, since each possible problem requires different treatments. Good luck.