Hello,
This looks like irritant contact dermatitis to the deodorants. Irritant dermatitis, the most common type of contact dermatitis, involves inflammation resulting from contact with acids, alkaline materials such as soaps and detergents, cosmetics, or other chemicals.
Avoid using any lotions, deodorants and creams for the meantime. Wash the area with a mild cleanser with moisturizing properties like Cetaphil. Then apply a good hypoallergenic moisturizer over the area and see if this improves. If the symptoms still persist then you can apply mild steroid like dermacort. Also take oral antihistaminic like Benadryl( may cause drowsiness).
If the irritation persists then please get it evaluated from a dermatologist. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I just took my 15 year old son into the doctors for the same thing. He said he'd never seen that before. He said to take 3-4 Advil/Motrin 3 times a day to see if it helps and then we'll look at it again in a few days. He said it resembles shingles/mild chicken pox (which he has been vaccinated for). My son said the same as you - that it has more of a burning feeling than an itch. He said it also shoots pain up the side of his neck. The doctor said that is because it's the nerve path for pain.
I'm having him eat well, drink LOTS of water to push it through, cut back on sports and heavy sweating for awhile and discontinue his fancy deodorant (I'll get some other kind from the health food store).
good luck and I'll keep you posted. Please do the same.