Medicated Oils During Pregnancy — What’s Safe, What Isn’t, and Why the Rules Are Strict

Pregnancy is a period where women are routinely told, correctly, that the safety rules are stricter than the rest of their life. Drugs that are fine on a Tuesday afternoon are contraindicated in the first trimester. Supplements that are unregulated in adults are quietly avoided by obstetricians. And traditional Chinese medicated oils — Tiger Balm, Wong To Yick, Po Sum On, Yu Yee Oil, White Flower Embrocation, and the dozen other bottles in the average Hong Kong medicine cabinet — sit in a grey zone that most pregnant women have never seen clearly explained.

The grey zone exists because the evidence base is thin. No pregnant woman has ever been enrolled in a randomised controlled trial of topical Tiger Balm. The data we have is a mix of animal studies (usually with implausibly high doses), case reports (selection-biased toward severe outcomes), and extrapolation from the pharmacology of individual ingredients. This article assembles that evidence into a practical set of rules, gives you the reasoning behind each one, and explains why the answer for Chinese and Hong Kong women is slightly different from the answer for Western women.

The general principle

Every chemical that crosses skin or mucous membranes to any meaningful degree can in principle reach the placenta. The placenta is an excellent barrier for large protein molecules and a relatively permeable one for small, lipophilic organic compounds. Camphor, menthol, methyl salicylate, borneol, eucalyptus oil, clove oil, and essentially every active ingredient in traditional medicated oils are small, lipophilic molecules that can cross the placenta in proportion to maternal blood levels.

The question is not whether they cross the placenta but whether the typical topical dose produces maternal blood levels high enough to matter for the fetus. For most adult topical uses of medicated oils, the answer is: probably not, but the margin is narrow, and pregnancy is not the time to push against margins.

First trimester — the most conservative period

The first trimester (weeks 1-12) is the period of organogenesis — when fetal organs are forming. This is the window when teratogens cause the most damage, and it is also, unhelpfully, the period when women may not yet know they are pregnant. Most obstetric guidance groups recommend avoiding all non-essential topical medications in the first trimester, and this extends to medicated oils.

If you are actively trying to conceive or in the first trimester, default to avoidance. Paracetamol (acetaminophen) is the go-to for muscle aches, and rest/elevation/ice is the go-to for minor injuries. The Chinese medicated oil cupboard takes a 12-week holiday.

Second and third trimesters — cautious use of specific products

Weeks 13-40 are the period when most women experience the muscle aches, low back pain, leg cramps, headaches, and sinus congestion that make medicated oils tempting. The rules relax slightly but remain conservative.

Ingredients to avoid entirely throughout pregnancy

Camphor (all trimesters, all doses): Camphor crosses the placenta. Animal studies at high oral doses show fetal toxicity. There are case reports of neonatal toxicity when mothers used high-dose camphor preparations late in pregnancy. The FDA formally recommends against using camphor-containing products during pregnancy. This includes all the major Chinese balms: Tiger Balm Red (25% camphor), Tiger Balm White (11%), Wong To Yick (15%), Po Sum On (16%), White Flower Embrocation (15%), and many TCM plasters.

Borneol (all trimesters): Chemically and pharmacologically similar to camphor. Traditional Chinese medicine considers borneol contraindicated in pregnancy (“龙脑香孕妇忌服”), and this prohibition has centuries of empirical history. Avoid.

Methyl salicylate in the third trimester: Methyl salicylate converts to salicylic acid, a salicylate related to aspirin. Third-trimester aspirin-like drugs are contraindicated because they can cause premature closure of the ductus arteriosus in the fetus, fetal bleeding, and delay of labour onset. Topical methyl salicylate in small amounts has not been definitively shown to reach fetal-relevant plasma levels in the third trimester, but the risk-benefit calculation is not favourable. Avoid Tiger Balm Red, Bengay, Icy Hot, Salonpas, and other methyl salicylate products completely in the third trimester. In the second trimester, avoid large-area or high-concentration application; small amounts on a localised area probably carry acceptable risk but should be discussed with the obstetrician.

Evening primrose oil, parsley oil, pennyroyal, blue cohosh: Several traditional herbal oils are uterotonic — they stimulate uterine contractions and can cause miscarriage or premature labour. These are not typically found in the big-name Chinese medicated oils, but they do appear in some traditional Chinese and Southeast Asian “pregnancy support” oils, which is paradoxical and dangerous. Avoid any herbal oil marketed for pregnancy-related symptoms unless specifically recommended by a qualified obstetrician or midwife.

Castor oil, especially orally: Castor oil has been used folklorically to induce labour. This is not safe. Avoid oral castor oil entirely during pregnancy unless specifically directed by an obstetrician at full term.

Ingredients that are probably safe in moderation

Menthol in low to moderate topical doses is probably safe throughout pregnancy. Menthol is metabolised by glucuronidation, which does not typically produce harmful intermediates. There are no strong reports of menthol-related pregnancy complications at normal topical doses. Menthol cough drops, menthol inhalers, and menthol lip balms are generally considered safe.

Eucalyptus oil in small amounts is probably safe in pregnancy at normal topical or inhaled doses, though oral eucalyptus oil is dangerous and should be avoided.

Peppermint oil is considered low-risk during pregnancy at normal doses. Peppermint tea, peppermint essential oil diffused, and peppermint topical at small amounts are generally considered safe.

Ginger (either oral or topical) is actually recommended in small doses for pregnancy-related nausea. Ginger oil and ginger tea are both considered safe.

Lavender oil is widely considered safe in pregnancy in small topical or diffused amounts, though very high-dose exposure is not studied.

Pure menthol products without camphor (rare in Chinese balms but common in Western products like Mentholatum original, some chest rubs, and cooling hair pomades) are probably acceptable in pregnancy at normal doses.

Ingredients with uncertain or middling evidence

Clove oil (eugenol): probably safe in small amounts but not recommended in large doses. Avoid clove oil in dental emergencies during pregnancy unless under a dentist’s supervision.

Cinnamon oil: avoid high concentrations; small amounts in finished products are probably fine.

Rosemary oil: large doses are traditionally contraindicated in pregnancy (“emmenagogue” — said to stimulate menstruation); small amounts in topical products are probably fine.

Tea tree oil: probably safe topically in small amounts; avoid oral use.

Product-by-product guidance

Tiger Balm Red: Contains camphor 25%, methyl salicylate 10%. Avoid throughout pregnancy. Camphor is contraindicated at any stage; methyl salicylate is contraindicated in the third trimester.

Tiger Balm White: Camphor 11%, menthol 8%, clove oil, cajuput oil. Avoid throughout pregnancy due to camphor content. The menthol alone would be fine but the camphor makes the product unsuitable.

Wong To Yick Wood Lock Medicated Oil: Camphor ~15%, menthol ~16%. Avoid throughout pregnancy due to camphor.

Po Sum On: Menthol ~16%, camphor ~16%. Avoid throughout pregnancy due to camphor.

Vicks VapoRub: Camphor 4.8%, menthol 2.8%, eucalyptus. Camphor concentration is lower than Chinese balms. The manufacturer and the US FDA classify VapoRub as category C in pregnancy (use only if benefit outweighs risk). Most obstetricians will tell pregnant women that occasional small-area application (e.g., a teaspoon-sized amount on the chest for a cold) in the second or third trimester is probably fine, but daily liberal use is not recommended.

White Flower Embrocation (白花油): Camphor 15%, menthol 15%, eucalyptus, lavender. Avoid throughout pregnancy due to camphor.

Yu Yee Oil (幼幼油): Various formulations, typically containing menthol, fennel oil, peppermint oil, and often a small amount of camphor. Avoid throughout pregnancy due to camphor content and uncertain composition.

Salonpas patches: Methyl salicylate 6-10%. Avoid in the third trimester; use cautiously in the second trimester (small patches only, short duration, not across joints that cover large skin areas).

Bengay, Icy Hot: Methyl salicylate 15-30%. Avoid throughout pregnancy due to high methyl salicylate content.

Peppermint oil (pure): In small amounts for nausea, muscle aches, or as a diffused aroma, considered safe throughout pregnancy.

Lavender oil (pure): In small amounts diffused or applied topically, considered safe throughout pregnancy.

Ginger oil or ginger tea: Safe and actually recommended for nausea.

Common pregnancy symptoms and the appropriate response

Muscle and joint aches (very common in second and third trimester as the body changes):

Preferred: Rest, warm compresses, pregnancy-safe massage, gentle stretching, prenatal yoga, paracetamol if needed.
Avoid: Tiger Balm / Wong To Yick / Po Sum On / camphor-based rubs; Bengay / Icy Hot / methyl salicylate rubs (especially third trimester); oral NSAIDs.
Probably OK in moderation: Pure menthol roll-ons (without camphor); topical magnesium; heat patches without active chemicals.

Headaches (common in first and second trimester):

Preferred: Hydration, rest, cold compress to forehead, paracetamol if needed.
Avoid: Camphor/menthol forehead rubs; peppermint oil applied to temples in the first trimester (just to be conservative).
Probably OK in second/third trimester: Small amount of peppermint oil to temples.

Cold and sinus congestion:

Preferred: Saline nasal rinses, humidifier, rest, hydration, paracetamol.
Avoid: Whole-chest rubs with camphor products (Tiger Balm, Vicks VapoRub at daily large doses).
Probably OK: Vicks VapoRub in small amounts on chest once or twice per illness; menthol inhalers; eucalyptus oil in a diffuser.

Insect bites and itching:

Preferred: Cold compress, calamine lotion, oral antihistamines that are pregnancy-safe (loratadine, cetirizine).
Avoid: Camphor balms on bites, especially if multiple.
Probably OK: Tiny dab of menthol-only cooling gel for one bite.

Nausea and morning sickness:

Preferred: Ginger (tea, capsules, candies), small frequent meals, vitamin B6, obstetrician-prescribed anti-emetics.
Avoid: Wong To Yick oil applied to abdomen (traditional but camphor-containing).
Probably OK: Peppermint tea, peppermint aromatherapy, ginger oil aromatherapy.

Leg cramps (common in third trimester):

Preferred: Stretching, hydration, calcium and magnesium intake, warm bath, elevation.
Avoid: Methyl salicylate rubs on calves (especially third trimester).
Probably OK: Warm compress, gentle massage with plain carrier oil, pure menthol rub in small amounts.

Breastfeeding after birth

Once the baby is born and breastfeeding begins, the rules relax but are not eliminated. Many active ingredients pass into breast milk in small amounts. The key rules:

Do not apply any medicated oil to the breast itself — the baby will consume it during feeding.
Wash hands thoroughly after using any medicated oil before handling the baby.
Keep all products out of the baby’s immediate environment — topical application on the mother’s back, shoulder, or leg is usually fine; application on the chest near the feeding area is not.
Camphor products: some authorities recommend avoiding even topical use during breastfeeding due to transfer concerns. Pragmatically, small amounts applied to areas far from the breast are probably OK, but the conservative position is to wait until weaning before resuming daily use.
Methyl salicylate: same caution as camphor. Avoid large-area use while breastfeeding.

The Hong Kong-specific consideration

Hong Kong Chinese women are culturally accustomed to traditional medicated oils for a wide range of discomforts, and stopping for 12 months (pregnancy) or 12-24 months (pregnancy + breastfeeding) can feel like losing a comfort tool. The same is true for Taiwanese, Singaporean, Malaysian Chinese, and mainland Chinese women.

The alternatives are real and effective. Obstetricians can prescribe paracetamol, pregnancy-safe topical options, and physiotherapy referrals. Antenatal massage, heat, cold, rest, and stretching provide most of the symptomatic relief that medicated oils would. It is a temporary inconvenience, not a permanent loss.

Many Hong Kong women also receive advice from mothers, mothers-in-law, or aunts to use specific traditional products during pregnancy for morning sickness or back pain. Some of this advice is harmless (ginger tea, warm compresses), some is neutral (aromatherapy), and some is actively dangerous (camphor rubs, uterotonic herbs). When in doubt, ask the obstetrician — not the family elder. Physicians are accustomed to this cultural conflict and can give you clear, specific answers about the product you are asking about.

Practical bottom line

Throughout pregnancy: avoid all camphor, borneol, and high-concentration methyl salicylate products. This rules out Tiger Balm, Wong To Yick, Po Sum On, White Flower Embrocation, Yu Yee Oil, Bengay, Icy Hot, and most traditional Chinese and Southeast Asian balms.
In moderation: menthol, eucalyptus, peppermint, ginger, lavender, and tea tree oils at small topical or aromatherapy doses are probably fine.
First trimester: default to avoiding all topical medicated products where possible.
Third trimester: be especially strict about methyl salicylate due to fetal ductus arteriosus risk.
Breastfeeding: avoid breast-area application; wash hands before handling baby.
When in doubt: ask your obstetrician about the specific product. Do not rely on family elders, traditional practice, or label marketing claims.

The 9 months of pregnancy (and 6-12 months of breastfeeding) are a short window. The medicated oils will still be in the cupboard afterwards. Skipping them temporarily is a very cheap insurance policy against an uncommon but serious risk.

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 and is not medical advice. Pregnancy-specific medication decisions should be made with your obstetrician or midwife, who can account for your specific stage of pregnancy, your medical history, and the specific product in question.