The death of a British teen who screamed in agony and collapsed moments after coloring her hair has put the spotlight on D-I-Y dye.

Seventeen-year-old Tabatha McCourt from Lanarkshire, England, died in hospital after what medics suspect was a severe allergic reaction to p-phenylenediamine, or PPD, a chemical found in permanent hair dye, the U.K.’s Daily Mail reported.

McCourt, a veteran dyer, began pulling her hair and vomiting 20 minutes after applying the color at a friend’s house, according to  the story.

PPD allergies usually cause itchy, red and swollen skin on and around the scalp. But in very rare cases, even a small exposure can cause anaphylaxis, or death.

“Severe acute allergic reactions like this are very rare but not impossible” said Dr. Darrell Rigel, a clinical professor of dermatology at NYU Langone Medical Center. “If it happens, the first thing to do is take an antihistamine. And then get to an emergency room right away.”

Anaphylaxis is caused by a massive release of histamine – the same chemical that brings on hives. An overload of histamine causes blood vessels to dilate causing a dangerous drop in blood pressure. Anaphylaxis is also marked by confusion, difficulty breathing and swelling of the eyes and face.

The Daily Mail also described the case of 29-year-old Mariade Kelly, whose jet-black locks landed her in intensive care earlier this year.

“My eyelids had swelled completely shut, and I couldn’t see,” Kelly told reporters. “I was terrified.”

Although dye boxes come with allergy warnings urging users to test the product on a small patch of skin first, many dye-hards skimp to save time. And for people with severe PPD allergies, the skin test alone could trigger a deadly reaction.

Even for routine dyers who have taken and passed the patch test, small changes in ingredients could trigger allergies to once-benign products. Rigel said cosmetic users should take note of minor reactions and go for an allergy test to avoid a more serious episode later on.

“Usually, the first exposure sensitizes you but doesn’t cause the severe reaction,” he said. “If you know you’re allergic to something, you can avoid it.”