Why Essential Oils Behave Differently in Summer Heat (And How to Store Them the Right Way)
A Quick Summary
Heat and light speed up oxidation in essential oils, changing their scent and increasing the risk of skin sensitization over time, with citrus oils like lemon and sweet orange affected most due to their high limonene content [1][2]. Jojoba oil, the carrier used in How Majesstic Botanicals' roll-ons, is a liquid wax ester rather than a true oil, making it naturally resistant to oxidation and shelf stable at room temperature [3][4]. To protect a roll-on through summer, keep it out of direct sunlight, store it in a cool dry place, keep the cap tightly closed between uses, and use it within one to two years of purchase.
Essential oils are chemically active liquids, and heat speeds up the natural process of oxidation that changes their scent and reduces their shelf life. Citrus oils are especially heat and light sensitive, while a carrier like jojoba oil is naturally far more stable. Understanding this is the difference between a roll-on that still smells vibrant in September and one that's gone flat, or worse, more likely to irritate skin.
What Heat Actually Does to an Essential Oil
Essential oils are made up of dozens to hundreds of volatile aromatic compounds, many of them terpenes and terpene derivatives. These compounds are chemically reactive, and when exposed to heat, light, and oxygen over time, they undergo oxidation, a chemical reaction that alters their structure. Oxidized essential oils don't just smell different (often flatter, sometimes sharper or "off"), they can also form byproducts more likely to cause skin sensitization, particularly in oils high in certain terpenes like limonene, which is abundant in citrus oils [1].
This is a well documented concern in dermatology and cosmetic safety literature. A multi-center European patch-test study found that 3.8 to 6.5 percent of dermatology patients tested positive for a reaction to oxidized limonene specifically, even when the same patients showed no reaction to fresh, non-oxidized citrus material [1]. The International Fragrance Association (IFRA) has also set usage limits on citrus peel oils in leave-on products for this reason [2]. It's part of why quality, fresh sourcing and proper storage aren't just about scent quality. They're about skin safety, too.
Which Oils Are Most Heat Sensitive
Citrus oils (like Citrus Limon, lemon, or Citrus Aurantium Dulcis, sweet orange) are cold-pressed from the peel rather than steam distilled, and they tend to oxidize faster than steam-distilled oils. Sweet, sunny, and full of the terpene limonene, they're also the most vulnerable to changes in temperature [1][2].
Heavier, resinous oils like Boswellia Carterii (frankincense) tend to be more stable over time and less reactive to moderate heat exposure. Floral and herbaceous oils fall somewhere in the middle, generally more stable than citrus but still benefiting from cool, dark storage.
Why Jojoba Oil Is Different
The carrier oil used across HMB's roll-on line, Simmondsia Chinensis (jojoba) seed oil, isn't actually a true oil at all. Botanically, it's a liquid wax ester, which gives it a molecular structure that's naturally far more resistant to oxidation than typical plant oils [3][4]. This is one of the reasons jojoba is such a common choice as a carrier in botanical formulations: it helps protect the essential oils blended into it and has a notably long shelf life on its own, even without refrigeration [3].
How to Store Roll-Ons (and Any Essential Oil Product) in Summer
A few practical habits go a long way during the hottest months:
Keep roll-ons out of direct sunlight. A car dashboard, a sunny bathroom windowsill, or a beach bag in direct sun are the worst offenders. Even short, repeated exposure adds up over a season.
Store in a cool, dry place when not in use. A drawer, a bag out of the sun, or a cabinet away from a stove or heater is ideal. Refrigeration isn't necessary for jojoba-based roll-ons, but avoiding consistent heat above room temperature helps.
Keep the cap on tightly between uses. Oxygen exposure, not just heat, drives oxidation. A tightly capped roll-on loses far less aromatic quality over time than one left open or loosely closed.
Use within the intended timeframe. Even well stored, essential oil blends are best used within the window suggested on the product, generally within a year or two of purchase for roll-on blends in a jojoba base.
FAQ
Do essential oils go bad in heat? They don't spoil in the way food does, but heat accelerates oxidation, which changes their scent and can increase the likelihood of skin sensitization, particularly in citrus oils [1].
Which essential oils are the most sensitive to heat? Citrus oils, like lemon and sweet orange, are typically the most heat and light sensitive because of their high terpene (limonene) content [1][2]. Resinous oils like frankincense tend to be more stable.
Is it safe to leave a roll-on in a hot car? It's not recommended. Even occasional heat exposure in a hot car can accelerate oxidation over time, especially for citrus-forward blends, and may shorten the usable life of the product.
Does jojoba oil need to be refrigerated? No. Jojoba oil is a liquid wax ester, naturally resistant to oxidation, and shelf stable at room temperature when kept out of direct heat and sunlight [3][4].
How long does a roll-on blend typically last? Most essential oil roll-on blends in a jojoba base are best used within one to two years of purchase, and proper storage away from heat and light helps preserve that window.
Every HMB blend, from Breath of Life to Peace, Be Still, is built on an organic jojoba base specifically because of its stability, but a little extra care in August keeps any blend at its best.
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.
Written by Jessica Florence
References
[1] Matura M, et al. "Oxidized citrus oil (R-limonene): A frequent skin sensitizer in Europe." ScienceDirect. https://www.sciencedirect.com/science/article/abs/pii/S0190962202001500
[2] "Safety Assessment of Citrus-Derived Peel Oils as Used in Cosmetics." Cosmetic Ingredient Review. https://www.cir-safety.org/sites/default/files/cpeelo092014FR.pdf
[3] "Jojoba: Unlocking its benefits in Cosmetic Formulations." Formula Botanica. https://formulabotanica.com/jojoba-in-cosmetic-formulations/
[4] "Physical Characteristics of Tetrahydroxy and Acylated Derivatives of Jojoba Liquid Wax in Lubricant Applications." PMC. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5816853/
