The same thing happens to me! I used to never go out in the sun when I was younger because I would always burn to blisters and it was worse when I had sunscreen on. Then, when I was older, I tried using suntan oil just to see what would happen. I bronzed beautifully. Now, I always use it when I'm in the sun and sometimes I don't even tan, just stay pasty white. All this, and I live in Florida. Ha ha.
Hello,
It is very surprising that the area that you had applied the sunscreen got the sunburns while the other areas did not. It could be due to applying products which are one year old. Sunburn results when the amount of exposure to the sun or other ultraviolet light source exceeds the ability of the body's protective pigment, melanin, to protect the skin.
Apply cool compresses on the area and take bath with cool (not very cold) water. Do not scrub your skin or shave your skin and use a soft towel and gently pat your skin dry. Also use a sunburn Over-The-Counter remedy containing aloe vera and a light moisturizer or a dusting powder to relieve chafing. You can apply silver sulfadiazine (1% cream) on the skin except face and see if it helps. If the symptoms still persist then you should consult a dermatologist and discuss the option of dermabrasion or laser resurfacing.
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.