Well... I just posted a response about this in regard to another question...
You might be experiencing a latex allergy. Certain kinds of elastic (especially the cheaper brands) often contains latex. I have to spend more on bras and underwear, looking for the kind that do not have exposed elastic or uses a different type of stretchy material instead of elastic.
Here is info from Wikipedia (http://en.wikipedia.org/wiki/Latex_allergy) on
Irritant contact dermatitis and Type IV (allergic contact dermatitis) due to latex... You can decide if it is similar to your current reaction:
1.) Irritant contact dermatitis: It can also cause irritant contact dermatitis: The most common type of reaction. This causes dry, itchy, irritated areas on the skin, most often on the hands. It can be caused by the irritation of using gloves, or it can also be caused by exposure to other workplace products.
2.) Also known as allergic contact dermatitis. This involves a delayed skin rash that is similar to poison ivy with blistering and oozing of the skin (see urushiol-induced contact dermatitis). This type is caused by a naturally occurring latex protein. Type IV reactions are caused by the chemicals used to process the rubber. Patch testing needs to be done to verify which type of chemical triggers the reaction. Once the chemical is identified, then the person can choose products that are not processed with that chemical. Both natural rubber and synthetic rubber products may cause type IV reactions.
I am allergic to latex. However, I was not always allergic; the sensitivity develops due to repeated exposure and gets worse after each incident of exposure. I no longer have the simple 'rash reaction' (red, itchy angry rash where your skin is in contact with latex.) I know get flu-like symptoms which can interfere with my breathing (stage 2 congestion/coughing, not anaphylactic shock yet).
Like I said, the more exposure someone has, the greater the potential that they may develop a latex reaction. Here is some info on latex allergies (in regard to elastic):
The last link is good if you need help in finding latex free products. I've pasted in the brand info on undergarments:
Hygeia - Latex-free underwear
Decent Exposures (800-524-4949) - Latex-free elastic for bras, underwear, swim suits
Blue Canoe (888-923-1373) - Latex-free clothing
Vermont Country Store ###-###-####) - Latex-free socks
Dr. Leonard's Healthcare Catalog (800-785-0880) - Non-binding, latex-free cotton socks
TechSpun (800-392-8500) - Latex-free socks
Kathy Ireland cotton/lycra/nylon (Kmart)
Cotton socks without elastic
Cottonique (1-888-90-COTTON) - Latex-free bras, underwear, t-shirts & boxers. (for both men and women)