All anhydrous projects have a melting point, and this melting point is a big part of what determines the texture and skin feel of the product. Something like a facial oil obviously has a very low melting point, so the product is pretty much always melted (aka liquid). Products with higher melting points are typically formulated to melt or soften (to varying degrees) somewhere around body temperature.
Body temperature is ~37°C (98.6°F). Something like a lip balm is formulated to soften when pressed against the skin, but not melt. To this end lip balms contain wax, which have higher melting points that butters and fatty thickeners. Beeswax melts around 63°C (145°F), and when it is added to formulations in significant amounts (typically above 20%) it generally raises the melting point of the product above body temperature.
Products like whipped body butters are designed to melt slightly below body temperature; they typically get most of their structure from semi-firm butters like shea or mango (with melting points around 35°C/95°C) that are softened (the melting point is lowered) with liquid oils. These decadent butters are formulated to melt on contact with the skin, so they melt below 37°C (98.6°F).
A decent point of reference most people will be familiar with is cocoa butter; it melts right around body temperature. If you’ve handled cocoa butter (or eaten chocolate), you’ll know how quickly it melts when in contact with the skin. If something you’re using melts faster than that, the melting point is likely lower than body temperature. If something melts slower, its melting point is likely higher than body temperature. By comparison, coconut oil melts at 24°C (75°C). Think about how quickly that melts when it contacts your skin! This is a fairly simplistic way of looking at things, but it’s a decent estimator.
You can also look at the melting points of everything in your recipe. If the highest melting point in the formulation is 35°C, and everything else is lower, you can be pretty confident the end product will melt below 35°C. How much lower will depend on a lot of factors (how much of the 35°C ingredient is used? What else is in the formulation? etc.), but if that’s as high as it gets, you know the melting point can’t be higher than that.
You typically won’t find too many products with melting points around room temperature because this makes for quite unstable products. Where I live I the temperature in my kitchen is typically around 22°C, but in the summer it can easily climb up to around 30°C. That means the coconut oil in my cupboard is usually solid (since it melts at 24°C), but sometimes on a hot summer day I’ll open the tub and find it has either completely liquified, or has a few solid blobs floating in a pool of liquid oil. This isn’t the type of experience we want with our skin care products! You don’t want to discover that something that’s supposed to be liquid is solid or vice versa, or end up with some sort of peculiar semi-formed separating oily thing.
Now that we’ve talked about the melting points of our products, let’s bring weather into it. 37°C (98.6°F) is pretty darn hot, but certainly not an out-of-the-question temperature (even Calgary has had hotter days!), especially if you are leaving concoctions in the car, or if you’re shipping them and they’re being left in hot delivery trucks.
Your product does not care if the heat comes from the air surrounding it, the stovetop, the microwave, or your skin—if the temperature of your product exceeds its melting point, it will melt. If your product is designed to melt below body temperature, there is a very good chance it will melt in the summer heat, especially if you live somewhere very warm.
Generally speaking, I’ve found products that contain at least 15–20% wax don’t melt in ambient heat. I’ve taken products like that to Australia and Costa Rica, and left them in my hot car in the summer, and they’ve been fine. They soften, but they don’t liquify. Anything that gets its sole structure from butters or fatty thickeners like stearic acid is fair game for melting in easily achievable ambient temperatures.
Yes, you can raise the melting points of your formulations by including waxes, but this will impact your end product. You might not want it to be waxy. You’ll lose that melts-on-contact consistency of your body butter because the melting point is now higher than body temperature. The melting point of a product is part of how it feels on the skin, and you can’t alter one without altering the other.
I’ve definitely seen Etsy shops and small skin care brands that won’t ship certain products during the summer, so that’s one way to go about it. You could also look at formulating more lotions if you’re concerned about melting, as they tend to be more thermally stable.
Something I’d love to do someday is spend a month or more somewhere properly hot and try formulating with more waxes and thickeners and see if the consistently increased ambient temperature impacts my perceptions of the skin feel. It could be that if you’re living somewhere with weather consistently warmer than body temperature things change a lot! I just haven’t had the chance to find out yet 🙂
Posted in: General Usage