Hello, this is Dr. Jess. I am sorry to hear about the problems with your pup. Allergies can be a very frustrating situation to deal with in our pets! It sounds like your dog likely has a secondary skin infection due to allergies if he has crusty lesions on the skin. This happens because the natural protective barrier of the skin is reduced with allergies and bacteria are more easily able to get below the surface of the skin. Almost always, this requires treatment with an antibiotic, usually for at least 3 or 4 weeks depending on how deep the skin infection is. Oftentimes a course of steroids is needed initially to reduce the itching and inflammation as well. If this is the first time your pet has had a breakout like this, it is harder to determine the cause. There are basically 2 main types of allergies in dogs. Food allergies (we can see them develop at any age and even if the dog has been eating that food their whole life). Food allergies are year round since they are always eating the food. Allergies to environmental allergens such as grasses, pollens, trees, etc. are the other type and often theses area seasonal. There is not test for food allergies other than putting your dog on a strict diet trial usually for 6 to 8 weeks to see if the skin improves. There are prescription diets your vet can prescribe for this, or you can cook your own diet if you don't wish to purchase the food. The allergies to the environment can be tested for and allergy shots can be used in severe cases. Since this is the first time (it appears) that this has happened with your pup, you may not need to jump to that yet. There are a few things you can try at home to see if you can decrease the occurrence of the environmental/seasonal allergies. The first thing I would recommend would be to start him on a fatty acid supplement. These are usually available as gel caps that you can squirt onto their food, or as a liquid that you can squirt on the food. They area available at most pet stores, and the label should tell you how much to use based on their size. Most vet offices will also carry them and they usually aren't too pricey. The fatty acid supplement will help keep the skin moisturized and also has anti inflammatory effects. I would keep your pets on this year round. I would also consider starting your dogs on a daily antihistamine such as benadryl or zytrec at the beginning of whatever tends to be their "itchy season" . Starting it BEFORE they start breaking out, and keep them on it throughout whatever season of the year causes itching. Putting booties and shirts on the dogs before they go outside can also help, just by decreasing the amount they are coming into contact with allergens outside. Also wiping them down each time after they come inside, to decrease the amount of allergens on their skin. You can use baby wipes or just a wet washcloth/towel. The other thing you can do during those allergenic months is bathing them frequently to remove the allergens and bacteria. When we have dogs with allergies what happens is their natural protective barriers on their skin is reduced and so bacteria that normally wouldn't bother a pet with healthy skin can get past those barriers and cause problems like infections or hot spots. The thing you must make sure you do if you are bathing frequently though (2 to 3 times weekly) is to make sure you are using moisturizing product afterwards, so ensure they do not get dried out. You can also just bathe the area that is affected by the allergies if it is just one area (i.e. just the feet or just the belly). Your vets office should have shampoos and moisturizers available.
As I said initially, however, it sounds like your dog needs to be treated for a secondary skin infection first, and other treatments are not going to help unless we get rid of the bacteria (and sometimes yeast as well) first.
I hope this information may offer some ideas to you. Let me know if you have any other questions!