My problem with the simple coconut oil deodorant and bicarb soda sensitivity

Earlier this year I tried a homemade coconut oil deodorant recipe for the first time. It worked as a deodorant, by eliminating smells (yay!), but it wasn’t perfect. My climate introduced the first problem: coconut oil experiences both solid and liquid phases during a year in the tropics. The second problem is one I believe many people experience - sodium bicarbonate irritation.

I didn’t want to just assume the irritation was caused by the bicarb soda without conducting a little test.

The test

I started by applying pure coconut oil to my underarms as I would normally with a deodorant. I carried this on for the same length of time as it took me to experience the irritation, which was roughly the length of time it took to use up the whole pot of deodorant. And, I stunk. Coconut oil did not remove odour by itself. But the test was important!

I removed all ingredients except for coconut oil because I wanted to be sure exactly what ingredient was causing the irritation - essential oil could be the source as well.

After the coconut oil test period I made another pot of coconut oil but included one more ingredient - arrowroot flour - and tested this mixture for the same period of time.

The coconut oil and arrowroot mixture did not give me any irritation (it also didn’t stop odour completely). So I preceded to make another pot with all three main ingredients: coconut oil, arrowroot flour and bicarb soda. However, I did not use four teaspoons of bicarb soda as I did in the original recipe. Instead I only used one.

As I write this, I am nearly finished testing this formulation and I have no irritation yet. Better yet, it has been working to remove odour. It might not be sufficient for those who exercise a lot or sweat more, who might need the addition of more bicarb soda. I would suggest testing a little bit extra bicarb at a time. You might not need as much as the orginal recipe and then can reduce the chance of experiencing irritation.

Once I settle on an amount of bicarb soda that doesn’t cause irritation and also prevents odour, I will add back the essential oil and make sure this doesn’t also cause irritation.

Irritation caused by sodium bicarbonate

So why do people commonly report irritation (in my case itchiness and redness) from using sodium bicarbonate in deodorants? The skin has a normal acidic pH of 4-6, that is important for skin barrier homeostasis, stratum corneum integrity and microbial defense.^1,2,3,4 The underarms are on the higher end of this range.⁵ Sodium bicarbonate, on the other hand, has a pH of 8-9 in aqueous solution.⁶ Elevations in normal skin pH have been shown to disturb the skin barrier^1,7 and it is possible that the addition of sodium bicarbonate could increase the skin pH enough to, over an extended period of application, cause irritation due to a disturbed skin barrier.

One study⁷ showed that a single-time increase of skin pH (in mice) did not produce inflammation or alter epidermal morphology, but it did result in a deterioration of stratum corneum integrity and cohesion. Interestingly, normal stratum corneum desquamation involves two enzymes that have a neutral pH optima (higher pH than acidic pH).^7,8

Melting temperature of coconut oil

Now, my next problem comes despite the presence of sodium bicarbonate. Using coconut oil as the foundation ingredient in my tropical climate causes the deodorant to be solid during the winter months and liquid during the summer months. This is because the melting temperature of coconut oil is 25ºC.⁹

Because of this, I exchanged the original tub for a roll-on bottle during the summer. However, in winter, the deodorant began to harden and if I hadn’t finished my roll-on deodorant yet I had to sit the bottle in a hot water bath to melt the coconut oil so I could apply it!

Ultimately, I would like a deodorant that would work the same in all temperature ranges that I used it in. Fats, like coconut oil, are predominately made of fatty acid esters, types of lipids, and their melting temperatures are influenced by the composition of these fatty acids. A higher relative amount of saturated fatty acids, means a higher melting temperature, all else equal. Longer chain fatty acids also have higher melting temperatures compared to shorter chain fatty acids. Coconut oil contains mostly saturated fatty acids,⁹ but not enough to ensure it is solid in tropical summers. Beeswax on the other hand is mostly composed of wax esters,¹⁰another type of lipid that are esters of fatty acids and alcohols.¹¹ The melting temperature of beeswax is typically quoted as being between 62ºC - 65ºC, a physical property that depends on the chain length of it’s esters.¹² Developing a new deodorant formula with a wax, like beeswax, might ensure I have a solid consistency throughout the seasons.

Note: The term “fat” is also used to refer to all lipids in general, as opposed to just esters of fatty acids or, even more specifically, triglycerides.

Separation of ingredients

Because of the fact that coconut oil melts in the tropical summer, another problem was revealed: arrowroot powder is not soluble in coconut oil. Arrowroot powder, or starch, is mainly comprised of the polysaccaride, amylopectin.¹³ When the coconut oil became liquid, I found the arrowroot powder seperating from the oil and sinking to the bottom of the bottle or jar. To use it in it’s liquid state, I had to shake it vigorously, and I mean vigorously, beforehand. It worked, but it might get tiring...

My current solution

Before I make alternative deodorant formulations, I am just altering the original coconut oil recipe. Previously, I used the rough volume lines on measuring cups from the kitchen, which worked fine, but to achieve more accurate formulations I am using grams this time.

• 45g coconut oil
• 19g arrowroot powder
• 5g sodium bicarbonate
• 0.15g essential oil

If you add more sodium bicarbonate, use less arrowroot powder to keep similar consistency (if you add 5g of bicarb, use 5g less of arrowroot).

The bicarb irritation is addressed by adding less bicarb to the deodorant.

The coconut oil melting problem is addressed by using a roll-on bottle in the summer (and shaking before use!) and a tub/jar in the winter. Alternatively, if one replaces the coconut oil with an oil with a higher ratio of unsaturated fatty acid esters, like olive oil, it will remain a liquid even when the temperature gets colder. Keep in mind though, that because of the higher amounts of unsaturated fatty acid esters, olive oil can go rancid faster.

I actually prefer the liquid roll on version, so I will definitely try to formulate another deodorant in the future that is liquid all year around. I will also try to make one that is solid all year around, like a stick deodorant perhaps...

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