The Bag Ladies campaigned to make the town plastic-bag free earlier this year and there is now an agreement among most traders in the area to use more eco-friendly biodegradable bags.
Margaret Butler, of Old Town, picked up the bag after failing to notice that it was made of corn-starch. She said: "I must have wiped my mouth because my lower lip swelled and the front part of my tongue quickly followed. I was very red in the face and was having problems breathing. The person with me gave me an Epipen injection realising i was going into anaphylactic shock. I was in full panic."
Mrs Butler returned to Alliance Chemist in Valley Road on Tuesday, explained what had happened and asked for a plastic bag for her purchases.
She said: "I find the staff there friendly and extremely helpful."
Mrs Butler said the member of staff serving her told her there were a few plastic bags left and that she could have one but a pharmacist overheard and said as soon as the small supply of plastic bags they had was used up there would be no more in the pharmacy whatsoever.
She said: "He told me that no exceptions could be made because of the agreement.
"I explained that I could not provide my own bags because I am often house-bound and rely on other people to collect my prescriptions.
"He just kept going on about how there were no exceptions.
"It was apparent that he had not listened to a word I had said."
She said she feels that the plastic bag ban has gone too far: "The insistence of the Bag Ladies has meant I have been robbed of my democratic rights to freedom of choice."
Les Siddall of Mytholmroyd, a friend of Mrs Butler, collected the bag that caused the allergic reaction from the pharmacy. He said: "For a pharmacist to say that you have to make your own arrangements to someone like Margaret is ridiculous.
"Margaret should be given an option. If it happened again she might die."
A spokesperson for Alliance Pharmacy has confirmed: "A patient using our Valley Road branch in Hebden Bridge has reported an allergic reaction to the biodegradable corn starch bags used for holding prescription items.
"All complaints are taken very seriously and we are currently investigating the situation to ensure that it is resolved satisfactorily and that any further incidents are avoided."
Bag Lady Mandi Paramor said: "This is not a ban, it is a voluntary campaign to raise awareness about the problems of plastic in the environment.
"I applaud the chemist's bold step to use corn starch instead of plastic - every shop has the right to choose.
"It is unfortunate that Mrs Butler has had this reaction and I feel very sorry for her but it is the choice of the business. We live in a democracy and this is not a ban. It is the first time we've heard of this happening and we are sympathetic."