Almost every day I am recommending patients to use a heating liniment to help ease their pain. Common questions that people in pain ask me are: Is the liniment safe to use? Which liniment is the best? Which liniment should I buy? In this first article I will explore their history and the safety, focusing on a common ingredient, namely methyl salicylate.
Liniments can be thought of as coming in three types, namely heating liniments, medicated liniments and those that offer heat and medication. Liniments (also rarely known as embrocations) are liquids rubbed on the skin with aim of relieving pain, decreasing muscle stiffness, or helping in other ways. Sometimes they are called heat rubs, muscle rubs, sporting lotions, and balms. Some specifically aim to dilate the superficial small blood vessels (i.e. capillaries) in your skin which results in a red area of skin and so are called rubefacients
Some heat liniments, like Tiger Balm which originated in Myanmar (Burma) are nearly one hundred years old and have a very waxy feel, (i.e. they have a high viscosity). Tiger Balm Ultra states that the active Ingredients are Camphor, and Menthol, and the inactive Ingredients are Cajuput Oil, Dementholized Mint Oil, Clove Oil and Cassia Oil in a paraffin base.
Australia has produced a number of original heat rubs, including Goanna oil / Goanna salve which was first sold in 1910. Although it was originally made from the fat of Goanna’s, it has been many years since the animal was hunted for this purpose. It is now made of Today’s Goanna Salve is made from Methyl Salicylate, oil of wintergreen, Turpentine oil, Camphor, Peppermint oil, Pine oil, Pumilio and Menthol.
Many liniments use methyl salicylate which has the formula C6H4(OH)(CO2CH3). Lots of plants produce this chemical, including those called wintergreens. The chemical appears to be metabolised (changed) in our bodies into salicylic acid which can then receive pain and inhibit inflammation.
In one study, the people rubbed 5 g (a teaspoon) of liniment containing 12.5% methyl salicylate into their skin twice a day for 4 days. They took urine samples from the people periodically and found after the first day over 15% of the methyl salicylate rubbed into the skin could be found in their urine, while after the second, third, and fourth days it was over 20%. The authors concluded that:
A considerable amount of salicylic acid may be absorbed through the skin after topical application of methyl salicylate products and this may increase with multiple applications.
Rubbed into your skin in low concentrations it is usually safe. There are some people though that have an allergy to methyl salicylate (or Aspirin) and so they should avoid these chemicals.
A teaspoon (5 ml) of wintergreen oil contains about 7 g of salicylate. Aspirin also contains salicylate with a per tablet dose often containing 350 mg. If you swallowed one teaspoon of wintergreen oil you would receive the same, possibly fatal, dose of salicylate as 20 Aspirin tablets. A lethal dose of Aspirin is about 500 mg per kilogram of body weight.
Given that Goanna oil consists of only 4.2% methyl salicylate, then you would have to swallow a significant amount before it would kill you. I’ve seen products with concentrations of methyl salicylate as high as 15% (Ax Brand Medicated Oil). Anyone with an aspirin allergy, or taking blood thinners for various problems such as blood clotting diseases, should consult a doctor before regularly using topical medications that contain salicylates. This is because, as mentioned above, methyl salicylate can be absorbed through the skin.
There are many factors to consider, but this response will only focus on methyl salicylate, and then only on what dose could be fatal as opposed to what dose might cause some harm to some people.
As one teaspoon of fluid equals about 5.0 ml. At a concentration of 4.2% methyl salicylate, 1 teaspoon of Goanna oil only contains 0.21 ml of methyl salicylate. If a person weighs 70 kg then a deadly dose of Aspirin is 35,000 mg, i.e. 35 grams. As 35 grams divided by 0.21 equals 166, then you would need to rub 166 teaspoons into your skin to achieve this dose. But even that is not the entire story, as not all of the methyl salicylate that you rub on your skin will be absorbed into the body. It is possible that only 20% is absorbed through the skin, so you would then need to rub in:
0.21 x 0.20 = 0.042;
35 divided by 0.042 equals 833.
In this scenario you would need to apply 833 teaspoons of Goanna oil (about 4150 ml or 4.15 litres) to achieve a deadly dose.
We sell and use Flexall Pain relieving gel Vitamin E enriched, as well as other liniments. Here is what some Flexall products contain according to various websites:
Inactive Ingredients: Allantoin; Aloe Barbadensis Leaf Juice; Carbomer; Eucalyptus Globulus Leaf Oil; Glycerin; Mentha Piperita (Peppermint) Oil; Methyl Salicylate; SD Alcohol 40 (15% W/W); Steareth-2; Steareth-21; Thymus Vulgaris (Thyme) Oil; Tocopheryl Acetate; Triethanolamine; Water Ingredients: Active Ingredients: Menthol (7%). Purpose: Topical Analgesic. Inactive Ingredients: Allantoin, Aloe Barbadensis Leaf Juice, Carbomer, Eucalyptus Globulus Leaf Oil, Glycerin, Mentha Piperita (Peppermint) Oil, Methyl Salicylate, SD Alcohol 40 (15% w/w), Steareth-2, Steareth-21, Thymus Vulgaris (Thyme) Oil, Tocopheryl Acetate, Triethanolamine, Water.
https://patient.info/doctor/salicylate-poisoning https://www.healthline.com/health/aspirin-overdose#overdose https://www.health.harvard.edu/pain/rubbing_it_in https://www.ebs.tga.gov.au/servlet/xmlmillr6?dbid=ebs/PublicHTML/ pdfStore.nsf&docid=755873DAE20ED5A9CA2577DD000242B0&agid=(PrintDetailsPublic )&actionid=1
https://www.walmart.com/ip/4-Pack-Flexall-Gel-4-oz/114995125 for flexall Pain Relieving Gel Vitamin E enriched.
Australian Government Department of Health, Therapeutic Goods Administration: Flex-all 454 Pain relieving gel https://www.ebs.tga.gov.au/servlet/xmlmillr6?dbid=ebs/PublicHTML/ pdfStore.nsf&docid=755873DAE20ED5A9CA2577DD000242B0&agid=(PrintDetailsPublic )&actionid=1
Note: Aspirin is made of acetylsalicylic acid https://www.walmart.com/ip/Flexall-Vitamin-E-Enriched-Pain-Relieving-Gel-4-Oz/ 46120158