Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzyme deficiency. It affects approximately 400 million people worldwide, with the highest prevalence in Southern Chinese, Southeast Asian, African, Middle Eastern, and Mediterranean populations. In Hong Kong, the prevalence among Chinese newborn males is roughly 4-5%; Hong Kong has had a universal G6PD newborn screening programme since 1984, which is why almost every Hong Kong parent of a G6PD-deficient child knows the diagnosis and receives a list of substances to avoid.
That list, distributed by Hospital Authority maternity wards and community clinics, typically includes mothballs, fava beans, certain antibiotics — and “Chinese medicated oils, balms, and herbal products containing certain camphor, menthol, and related compounds.” The wording is deliberately cautious because the evidence is imperfect, and parents often don’t know which specific products to avoid and which are probably safe.
This article explains what G6PD deficiency actually is, which ingredients in traditional Chinese and Southeast Asian medicated oils carry real risk, which are theoretical concerns, and how a G6PD-affected family should think about the cupboard of Tiger Balm, Wong To Yick, and Yu Yee Oil that is still standard in most Chinese households.
Glucose-6-phosphate dehydrogenase is an enzyme that catalyses the first step of the pentose phosphate pathway. That pathway produces NADPH, which is the primary reducing agent red blood cells use to neutralise oxidative stress. In cells with normal G6PD, oxidative damage from environmental toxins, drugs, and infection is efficiently neutralised. In cells with deficient G6PD, oxidative stress cannot be buffered — the red cells accumulate damage, their membranes become fragile, and they break apart (haemolysis).
The clinical picture ranges widely by severity of the enzyme deficiency:
Symptoms of acute haemolytic crisis typically appear 24-72 hours after exposure and include:
In neonates, G6PD deficiency is a major cause of severe prolonged jaundice that can lead to kernicterus (brain damage from bilirubin) if not managed. This is why neonatal screening is so important.
The Hong Kong Hospital Authority’s universal newborn screening (since 1984) has built a culture of awareness that does not exist in most Western countries. Hong Kong parents typically receive:
The cultural weight of this information is significant. Grandparents and relatives often react strongly when told a grandchild has G6PD deficiency — “不能聞樟腦” (cannot smell camphor) is folk shorthand that is sometimes overstated and sometimes undersold. The reality is more nuanced than the folk wisdom, and parents deserve to know which products carry real risk and which carry theoretical risk.
Naphthalene mothballs are the classic, well-documented trigger for G6PD haemolysis. This is not a medicated-oil ingredient directly, but it matters because many older Chinese households stored clothes and blankets with mothballs, and infants swaddled in such cloth can absorb naphthalene through skin and inhalation, causing severe haemolysis.
Modern camphor mothballs (1,4-dichlorobenzene or natural camphor) are safer than naphthalene but are frequently confused with it, which is why any mothball is treated cautiously in G6PD households.
Rule: No naphthalene mothballs in any G6PD household. Ever. If you don’t know which type is in your wardrobe, replace them.
Camphor is the primary concern for medicated oil users with G6PD deficiency. The evidence is mixed:
Practical position: Avoid all significant exposure to camphor-containing products in G6PD-deficient infants and children. Adult G6PD-deficient individuals may tolerate small topical amounts on small intact skin areas, but they should be aware of the risk and watch for signs of haemolysis (dark urine, jaundice, fatigue) after use.
Menthol is metabolised primarily by glucuronidation, which does not generate significant oxidative stress. Menthol alone is probably low-risk for G6PD patients, and there are very few case reports of menthol-triggered haemolysis.
However, menthol products rarely contain menthol alone — they usually pair menthol with camphor, methyl salicylate, or essential oils. Tiger Balm White is ~8% menthol but ~11% camphor. Wong To Yick is ~16% menthol plus ~15% camphor. In these combination products, the camphor is the concerning ingredient.
Practical position: Menthol alone is probably safe in moderation for G6PD adults; pure menthol cooling lotions and menthol-only cough drops should be fine. Menthol products combined with camphor or other terpenes should be treated as camphor-containing products.
Methyl salicylate (oil of wintergreen) is metabolised to salicylic acid, which is chemically similar to aspirin. Aspirin itself is NOT typically on G6PD avoid lists — salicylates are generally considered safe for G6PD at normal therapeutic doses. However, high-dose salicylates can cause oxidative stress and have been weakly associated with haemolysis in severe G6PD variants.
Topical methyl salicylate rubs in moderate amounts for adults are probably safe for G6PD carriers. Large-surface-area application or combined use with aspirin raises the theoretical concern to a real one.
Practical position: Adult G6PD carriers using small topical amounts of Tiger Balm Red, Bengay, or similar methyl-salicylate products on small intact skin areas are probably safe. Avoid large-area use. Avoid all use in G6PD-deficient infants.
Eucalyptus oil (1,8-cineole / eucalyptol) is not on the standard G6PD avoid lists and there are no strong case reports of eucalyptus-triggered haemolysis. The main safety concern with eucalyptus is seizure risk in children (from ingestion), not G6PD.
Practical position: Probably fine for G6PD carriers at normal topical doses.
Borneol is a terpenoid chemically very similar to camphor, commonly used in traditional Chinese medicine and in many Southeast Asian balms. It probably shares the same oxidative metabolism as camphor.
Practical position: Treat borneol-containing products the same as camphor-containing products. Avoid in infants; adults use cautiously.
Peppermint oil is primarily menthol, and like menthol is probably low-risk for G6PD. There are no strong reports of peppermint-triggered haemolysis. Note that peppermint candies, peppermint mouthwash, and peppermint essential oil are all probably fine for G6PD carriers in normal doses.
Clove oil contains eugenol, which has weak oxidative potential and has been associated with very rare haemolytic events in case reports. Most G6PD lists do not include clove oil specifically, but caution is reasonable, especially for infants and for large-dose exposures.
Wintergreen essential oil (almost pure methyl salicylate) is a toxicity concern for all users, not just G6PD. See the methyl salicylate section above. Same rules apply.
Tiger Balm White: contains camphor ~11%, menthol ~8%, clove oil, cajuput oil, mint oil. For an adult G6PD carrier: probably safe in small amounts on small intact skin areas, avoid daily large-area use. For G6PD infants: avoid entirely.
Tiger Balm Red: contains camphor ~25%, menthol ~10%, methyl salicylate ~10%, cassia oil. Higher camphor concentration than White. Adults: use sparingly; avoid under occlusion. Infants: avoid entirely.
Wong To Yick Wood Lock Medicated Oil: camphor ~15%, menthol ~16%, methyl salicylate content varies. One of the most popular HK brands. Adults: small amounts on small areas are probably safe; avoid daily liberal use. Infants: avoid entirely.
Po Sum On: menthol ~16%, camphor ~16%, lavender oil, dragon’s blood. Adults: similar guidance — small areas, small amounts, avoid daily liberal use. Infants: avoid entirely.
Vicks VapoRub: menthol 2.8%, camphor 4.8%, eucalyptus. Lower concentrations than the Chinese balms. Adults with G6PD are probably safe for adult chest-rub use. Infants (including non-G6PD infants) are already contraindicated by the manufacturer — don’t use on any infant.
Yu Yee Oil (幼幼油): the traditional Chinese “baby wind oil” given for infant colic. Contains menthol, fennel oil, peppermint oil, and in many brands a small amount of camphor. This is the product that causes the most anxiety in HK G6PD parents. The honest answer: low-camphor formulations used in tiny drops for babies are probably OK, but there is no strong evidence either way. Many HK paediatricians now recommend G6PD parents avoid it entirely because even a small relative risk is not worth it when safer alternatives (warm tummy massage, simethicone) exist.
White Flower Embrocation (白花油): camphor ~15%, menthol ~15%. Treat as Wong To Yick — adults cautiously, infants not at all.
Chinese herbal plasters (狗皮膏, 活血膏藥): extremely variable in content. Many contain camphor, borneol, menthol, methyl salicylate in combination. If the product does not clearly list ingredients or you are buying from a TCM shop, assume it contains camphor and borneol, and treat with the same caution.
For G6PD-deficient individuals deciding whether to use a given medicated oil, the practical rule is:
Infants and children under 6 years: Avoid all camphor, borneol, and methyl-salicylate-containing products entirely. Menthol-only products (rare) are probably OK but unnecessary.
Children 6-12 years: Avoid camphor and borneol. Methyl salicylate products only on very small areas for short periods, if at all.
Pregnant G6PD carriers: The fetus may also be G6PD-deficient. Avoid all camphor and borneol products during pregnancy. Low-concentration menthol topical is probably safe.
If a G6PD-deficient person uses a medicated oil product and then develops signs of haemolysis within 24-72 hours:
Most haemolytic episodes from topical medicated oils are self-limited and resolve with cessation and supportive care. Severe cases requiring transfusion are rare but do occur, particularly in infants.
In Hong Kong Chinese families, grandparents often have decades of experience using traditional medicated oils and are the default caregivers for young grandchildren. Many grandparents learned to rub babies with 風油 (wind oil) or Yu Yee Oil for colic, crying, insect bites, or simply as a comforting ritual. When a grandchild is diagnosed with G6PD deficiency, the grandparent may not understand why this long-established practice is now forbidden, may disagree with “the doctor’s advice”, and may quietly apply the oil anyway when the parents aren’t watching.
This is a real and documented cause of infant haemolytic crises in Hong Kong. The solution is not confrontation but education — explain the mechanism in age-appropriate terms, provide written reference material in Chinese, and emphasise that the avoidance is not a rejection of tradition but a specific medical necessity for this particular child. Many grandparents, once they understand, become the strictest enforcers.
This article is part of the Medicated Oil Knowledge Hub, a free educational reference on traditional Chinese and Southeast Asian herbal medicated oils. Information here is for education; it is not medical advice. G6PD deficiency management should be individualised with your paediatrician, GP, or haematologist. In Hong Kong, the Hospital Authority’s newborn screening programme provides formal counselling and a written avoid list — trust that list first.