A young woman from Belfast has claimed she developed a bald patch, blisters and sores as a result of regularly using 'dry' shampoo.
Nicole Baxter was initially diagnosed with triangular alopecia - hair loss in one area of the head.
The 21-year-old wrote on Facebook in a post shared 31,000 times: "Dry shampoo caused me to have a bald patch on my head, which I still have, and it may or may not grow back, but nothing can be done - and a terrible scalp for ages."
The former Victoria College student went to her GP at the end of last year.
"My scalp was also very itchy and flaky," Nicole posted.
"I had wee red sores and blisters all over my scalp and a terrible burning sensation all over my head, to the point where I would wake up several times a night due to the discomfort and pain."
She was referred to the dermatology unit in Belfast City Hospital and was diagnosed with the hair-loss condition in February.
Nicole was told to come back for a follow-up procedure last Thursday, but not to have anything in her hair.
When she arrived, she said the specialist "looked at my file and said that it was to see what the blisters and sores were and could they diagnose a cause."
It was only then Nicole realised they had gone.
"So, she compared my scalp today to the pictures that were in my file from February and asked what had I done differently in the last six/seven weeks that may have helped it?" she wrote. "I told her I'd stopped using dry shampoo and that was it, nothing else different."
Nicole now advises people to avoid dry shampoo, although she acknowledges she had an unusually severe allergic reaction.