An experienced Tauranga hairdresser says consumers should always skin-test hair dye before using it.

The warning comes after an online posting of a one young woman who didn't take precautions before colouring her own hair, and suffered a severe allergic reaction.

The online hair disaster in various stages. Photos: THECHOSENSINGER/IMGUR.

According to pictures posted online, it took five days for the reaction to die down. The photos, uploaded to Imgur by a user called thechosensinger, show the women with her face and head so swollen they're a completely different shape.

Hair to Train general manager Donna Waterson says while the online picture was an extreme result, she says doing a skin test prior to dying hair is essential.

The company has been running since 1997, operating from their site on Anson Street, and is the largest training academy in the Bay of Plenty.

Donna says all of their clients must do a skin test before any dye is put on their hair.

'We have skin tested our clients for the past seven-and-a-half years,” she explains.

'Our policy is very clear. No skin test, no colour. A client must have a skin test every time she has a colour."

Donna says the policy is there to protect both the client and the stylist.

'It's a vital part of the service. People can use colours their whole lives and one day, out of the blue, react to a colour. That is why we do it every time. I would not risk this on anyone.”

Donna says they use professional products only.

'We use only professional products from Goldwell and it states clearly that a skin test must be done prior to any colour service.”

The general manager says it's an OSH regulation that all hairdressing salons do skin tests.

Before the hair dye incident.