[anonymously]

Did you check the search engine here? I do not agree with all of the opinions expressed. /forums/search/allergies/

Do not put anything on it, it will only make it worse.
Assuming your dog is in good health and has seen the regular vet recently.
The best choice would be to see a board-certified veterinary dermatologist, if one is available near you (here is a list: http://www.acvd.org/).

Most dermatologists will not skin test for allergies until the dog has been exhibiting symptoms for 1 year/4 seasons without any significant periods of relief. There are also other treatment options that a specialist could offer.

Don’t be fooled by mail-in saliva and hair tests, I have heard they are unreliable

A summary of treatments for canine atopy:

Evidence-Based Canine Allergy Treatment

And here is a recent update:

Evidence Update- Evidence-based Canine Allergy Treatment

More info here:
http://www.2ndchance.info/allergytesting.htm
Skin tests to determine what your pet might be allergic to are considerably more accurate, on the whole, than blood tests. However, they are not 100% accurate either. To have them performed, you will need to locate a board certified veterinary dermatologist

excerpt below from: http://www.2ndchance.info/Apoquel.htm
Food Allergies are probably over-diagnosed in dogs (they account for, perhaps 5-10%). Hypoallergenic diets are occasionally, but not frequently, helpful in canine atopy cases but you should always give them a try. Food intolerances are more common – but considerably more likely to result in digestive disturbances and diarrhea than in itching problems.

PS: If you wait, it may get really bad, keep an eye on the chest area for a bright red rash developing. When this happened to my dog I had to go to the emergency veterinary clinic. They usually prescribe steroids to stop the suffering and to temporarily get the situation under control. The Dr there reprimanded me for putting witch hazel on the rash. There are prescription creams that a dermatologist will prescribe that help, but usually only in conjunction with other treatments.