Oxidation: The Invisible Enemy
A formula is bottled crystal-clear, then weeks later it begins to yellow and its scent turns flat. The culprit is almost always the same: oxidation. When atmospheric oxygen combines with light and heat, the delicate molecules in a fragrance oil break down. When the top note fades, this layer takes centre stage — but in an oxidised formula, that stage has already decayed.
Oxidation hits citrus oils hardest (rich in terpenes: limonene, linalool) and natural fixed oils. The result is colour shift, a sour-metallic odour, and declining performance. Using an antioxidant delays this reaction — it does not stop it. An antioxidant is not a safety net; it is a brake that buys you time.
BHT and Tocopherol: Two Different Characters
Both antioxidants scavenge free radicals, but their temperaments differ. Labelling one as synthetic and powerful and the other as natural and gentle is an oversimplification — the choice depends on the structure of your formula.
BHT (butylated hydroxytoluene) is a potent, stable, synthetic antioxidant that performs at very low concentrations. It is colourless, contributes almost nothing to the scent, and dissolves well in both alcohol and oils. Tocopherol (Vitamin E) is derived from natural sources and is highly skin-compatible; however, it can itself oxidise over time, causing slight yellowing. Using both together is a common strategy.
A critical note here: the perception that "natural means safer" is incorrect. Safety depends not on origin but on the molecule and the use level. Tocopherol is natural but can cause colour issues at high doses; BHT is synthetic but performs reliably at low concentrations.
| Property | BHT | Tocopherol (Vitamin E) |
|---|---|---|
| Source | Synthetic | Natural (plant-derived) |
| Typical use level | 0.01–0.1% | 0.05–0.5% |
| Solubility | Oil + alcohol | Good in oil; limited in alcohol |
| Scent contribution | Negligible | Slight; noticeable at high doses |
| Colour risk | Low | Yellowing at high doses |
| Best suited for | Alcohol-based fragrance, oils | Oil-based products, balms, fixed oils |
Percentages are given relative to total formula weight (g/g). Test in small batches with your own formula and monitor colour and scent stability over several weeks.
When sourcing BHT, opt for laboratory-grade product — browse the product page for BHT options.
Dosage and Application Steps
What matters with an antioxidant is not so much how much you add but when and how you add it. A small amount is sufficient; more does not help — it only causes colour problems.
- Accurate weighing
BHT use levels are very low (around 0.05%). They cannot be measured by eye; a precision balance (0.001 g) is essential. First prepare a pre-solution in a small amount of fragrance oil/solvent, then incorporate it into the main blend.
- Add in the correct order
Add the antioxidant to the fragrance oil or oil phase before the alcohol phase. This way it immediately surrounds the hydrophobic (water-insoluble) components that need protection most.
- Distribute evenly
Even dispersion of a low-level ingredient throughout the entire volume is critical. Homogenise for several minutes using a magnetic stirrer; uneven distribution leaves unprotected pockets.
- Don't forget the g↔ml conversion
Fragrance oil densities vary widely (citrus ~0.84; heavy resins/synthetics >1.10). When transferring a gram-based formula into a ml-measured bottle, account for density — otherwise you risk overflow or under-filling.
- Test and observe
Store three separate samples under different conditions (dark room, in light, warm environment) and compare colour and scent changes. Use these observations to finalise your formula.
Your Primary Defence: Light, Oxygen, Temperature
An antioxidant is your second line of defence. The first is storage. Control these three variables and you will extend shelf life far more than any antioxidant alone can.
Light: UV radiation triggers oxidation reactions and accelerates colour change. Use amber or dark glass bottles and opaque packaging. Never leave a clear bottle under display lighting.
Oxygen: The larger the headspace in a bottle (headspace), the more air is present. Fill bottles close to the top and seal them tightly. Split large stocks into smaller bottles to prevent fresh air entering with every opening.
Temperature: Every 10°C rise noticeably increases reaction rate. A cool, stable, dark shelf is best. Window sills, radiator sides, and car glove compartments are off-limits.
Note: Maceration (the maturation of alcohol and fragrance oil) is carried out at room temperature in the dark; chilling and filtration are separate steps. We cover this in detail in our professional laboratory setup article.
FAQs and Summary
Combined with correct storage, an antioxidant preserves the colour and scent of your formula. Don't overdo it, weigh precisely, and store in the dark. The rest is your signature.
Should I use BHT or tocopherol?
If I use an antioxidant, can I leave my bottle in sunlight?
Will adding more antioxidant make my formula last longer?
Related Articles
Advantages of a Magnetic Stirrer: Homogenisation in Perfume and Cosmetic Production
The advantages of a magnetic stirrer over manual mixing: homogeneity, repeatability, heated models, hands-free operation
Read →Setting Up a Professional Perfumery Laboratory: Which Equipment Is Essential?
Core equipment for a fragrance/fragrance oil laboratory: precision balance (0.001 g), glass beakers and measuring cylinders, pipettes and auto
Read →Heated and Unheated Homogenisation Techniques with a Magnetic Stirrer
Stir bar selection, speed settings, when a heated plate is needed; dissolving viscous/solid fragrance oils
Read →