Heat Sensitivity of Plant Oils and Butters
When working with plant oils and butters in cosmetic formulations, one of the most critical factors to consider is heat sensitivity. Excessive heat can cause oils and butters to degrade, lose beneficial properties, and even go rancid. Understanding how to handle these ingredients during the formulation process ensures product stability, shelf life, and efficacy.
Why Heat Matters for Oils and Butters
Plant oils and butters are rich in unsaturated fatty acids, vitamins, and antioxidants. These beneficial compounds are sensitive to high heat. When exposed to temperatures beyond their stability threshold:
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Oxidation accelerates, causing oils to go rancid faster.
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Fatty acids break down, reducing the oil’s nutritive and conditioning properties.
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Natural antioxidants (like vitamin E) are destroyed, further reducing shelf life.
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Texture and aroma of the oil or butter may change, impacting the finished product.
For example, delicate oils like flaxseed or rosehip degrade quickly with heat, while more stable oils like coconut and shea butter can withstand moderate heating.
Determining the Right Temperature
Each oil or butter has an approximate maximum safe heating temperature for formulation. A practical guideline is:
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Delicate oils (high in polyunsaturated fatty acids): Add at cool-down phase (below 40°C / 104°F).
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Moderately stable oils and butters: Can be gently heated if needed, but ideally added below 45–50°C (113–122°F).
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Stable butters and saturated oils (shea, cocoa, coconut): Can withstand moderate heating during the oil phase (up to ~70°C / 158°F).
As a cosmetic formulator, always check the oil’s composition and plan which phase to add it to—heated oil phase or cool-down phase.
Heat Sensitivity and Iodine Value
In our blog post, Why a Cosmetic Formulator Needs to Know the Iodine Value in Plant Oils and Butters, we explained how the iodine value reflects the degree of unsaturation in an oil or butter. This directly links to heat sensitivity:
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High iodine value (e.g., flaxseed, chia, hemp): Very heat-sensitive, short shelf life. Must be added at cool-down.
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Moderate iodine value (e.g., sunflower, almond): Somewhat stable, mild heating is acceptable.
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Low iodine value (e.g., cocoa butter, coconut oil, shea butter): Heat-stable, longer shelf life.
The iodine value is a valuable tool for formulators to predict both oxidative stability and how much heat the oil or butter can withstand during formulation.
Download the Chart
Get a handy reference guide to use in your lab or studio. Download the chart “Heat Sensitivity of Plant Oils and Butters in Cosmetic Formulations” with iodine values and recommended safe temperatures for formulators.
Best Practices for Formulators
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Use a double boiler or water bath to gently heat oils when necessary.
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Keep delicate oils for the cool-down phase (below 40°C).
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Add natural antioxidants like tocopherols (vitamin E) to extend shelf life.
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Store oils and butters properly in cool, dark conditions to minimize pre-oxidation before use.
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Consult suppliers for recommended processing temperatures for specialty oils.
Conclusion
The heat sensitivity of plant oils and butters is a vital consideration for every cosmetic formulator. By understanding the relationship between heat exposure, rancidity, and iodine values, you can make better decisions about when to add oils and butters to your formulation. Proper handling preserves their integrity, ensures longer shelf life, and delivers maximum benefits to the skin and hair.
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