Hair dye allergy and diet: link to paraphenylenediamine

The primary allergenic component of hair dye allergy is p-phenylenediamine (PPD). There is currently no authoritative clinical evidence proving that daily diet will directly ingest PPD or induce PPD allergy. Only during the allergic attack period, high histamine and allergenic foods may aggravate the symptoms. Dietary adjustments can neither prevent PPD allergy nor replace regular anti-allergy treatment.

Don't believe it, when I was helping out in the dermatology clinic two years ago, I would meet three or four people a week who were allergic to dyeing their hair. Eight out of ten people would come in and the first thing they would say would be "Doctor, did I eat something wrong yesterday?" What impressed me most was an aunt in her 50s. The day after she dyed her hair black, her eyes were swollen to just a slit, and there were a bunch of blisters on her scalp. She insisted that the crayfish she ate the day before was the cause. It wasn’t until we did a patch test on her, which showed a strong positive for p-phenylenediamine, that she realized it was not on the dinner table at all.

Let’s talk about p-phenylenediamine itself. It is the core color-developing ingredient in permanent hair dyes. It has a small molecule and strong permeability. It can penetrate into the hair cuticles and bind firmly to keratin. The dyed color does not fade after two months of washing. The effect is really good, but it is also a "old nail" among cosmetic allergens. According to the cosmetics adverse reaction monitoring report released by the State Food and Drug Administration last year, about 90% of hair dye allergy cases are related to PPD. It induces delayed contact dermatitis. Many people only develop symptoms 1-3 days after dyeing, which coincides with eating hot pot, seafood, mango and other foods. Naturally, it is easy to blame the blame on diet.

Having said this, someone must ask, well, the last time I dyed my hair and ate something spicy, it did make the swelling worse. Doesn’t diet have any impact at all? This is actually the most controversial part of this topic right now. Traditional empiricists (including many clinical views of traditional Chinese medicine) will recommend that you avoid "eating foods" before and after allergies, and avoid touching seafood, beef, mutton, and spicy foods. This statement is actually not entirely unreasonable - the body's histamine level is already high during an allergic attack. Eating foods with high histamine levels or that are likely to trigger your personal sensitivity will indeed amplify the symptoms of redness, swelling, and itching, which is equivalent to adding firewood to the already burning inflammation. But let’s be clear: it is only an inducement to aggravate symptoms, and it is definitely not the cause of allergies. Even if you don’t eat a mouthful of food, PPD has been combined with the protein of your scalp, and you will still be allergic.

There is also a speculation that has become popular in recent years. It is said that long-term consumption of burnt meat and processed meat products. The heterocyclic aromatic amines in them have a similar structure to PPD. Will it cause cross-sensitization and make you more likely to be allergic to hair dyes? This is still in the in vitro cell experiment stage. Only a few research papers with small samples have mentioned the possibility. There is not enough human clinical data to support it. It is a hypothesis that is still being discussed in the academic circle. There is really no need to give up barbecue and sausages just for the occasional dye. It is not a mistake.

I have talked to many barbershop owners who have been in business for more than ten years. When they give reminders to customers before dyeing, they will add "If you have eaten something that usually makes it itchy after eating in the past three days, either wait for two days before dyeing, or remember to tell it in advance." This is not because they are afraid of food allergies, but because they are afraid that when there is slight redness and itchiness, they will not be able to figure out whether it is a problem with the dye or food, which will delay follow-up treatment. To put it bluntly, this is a matter of practical caution, not a scientific conclusion.

The most fearful thing is that many people have reversed the cause and effect. After being allergic, they dare not eat anything. They eat plain porridge with vegetables every day and dare not take medicine. They just carry it. Last month, a college student came to see a doctor. After dyeing his hair light blonde, he became allergic and his face was so swollen that he couldn't recognize the dormitory door. He kept his mouth shut for a week and didn't dare to touch anything delicious. As a result, the symptoms did not go away at all. He came to the hospital and was prescribed oral antihistamines and weak hormone ointment. It was almost gone in three days. When he left, he said aggrievedly that if he had known better, he would not have been hungry for so long.

As an aside, I met an aunt who had dyed her hair for 30 years. She had never had any allergies. Last year, the hair suddenly became swollen. When I asked, I found out that she had switched to a "pure vegetable black hair cream" sold by Wechat. When I looked at the ingredient list, I saw that the PPD was three times higher than the standard. It really doesn't mean that you are always safe if you haven't been allergic before. Domestic regulations now require that the content of PPD in hair dyes cannot exceed 6%. The European Union has included high-concentration PPD in the banned list. Many hair dye products that are mainly "purely natural" are actually just another word. PPD is hidden in the corner of the ingredient list. Be sure to double-check when buying.

To put it bluntly, hair dye allergy is most likely caused by paraphenylenediamine. Diet is at best an "accomplice" that adds fuel to the flames, and is never the main culprit. If you are really worried about allergies, check the ingredient list first to avoid PPD, and do a skin test behind the ears 48 hours before dyeing. It is more reliable than any taboos. If you are really unfortunate enough to be infected, you should take medicine and see a doctor when you should. Don’t go hungry because it is not worth the loss.