Short answer
Fragrance raw materials degrade mainly through oxidation, light, heat and evaporation. Expressed citrus oils and other materials rich in easily oxidized components change fastest; many resinoids, woods and stable aroma chemicals last much longer. Store materials cold, dark and in well-filled, tightly closed containers, record the date each was received and opened, and check them before use against a retained reference or your notes. Oxidation can also create skin sensitizers, so a degraded material is a safety concern, not just a quality one.
What makes materials degrade
- Oxygen. Many fragrance components react with air. Terpenes such as limonene, abundant in citrus oils, oxidize to compounds that smell different and can be more sensitizing than the original.
- Light. UV and visible light accelerate oxidation and other reactions. Clear glass on a sunny shelf ages materials quickly.
- Heat. Higher temperatures speed every reaction and increase evaporation.
- Evaporation. Volatile materials and alcohol dilutions lose their lightest parts each time the bottle is opened, changing both strength and character.
- Water and contamination. Moisture and stray material introduced by pipettes can start unwanted reactions.
Which materials age fastest
| Tends to age quickly | Tends to be more stable |
|---|---|
| Expressed citrus oils (bergamot, lemon, orange) | Many resinoids (benzoin, labdanum) |
| Conifer and other terpene-rich oils | Woody oils such as patchouli and sandalwood-type materials, which often improve with age |
| Some aldehydes, prone to oxidation | Many musks and stable aroma chemicals |
| Alcohol dilutions opened often | Well-sealed DPG dilutions of stable materials |
Suppliers often state a shelf life or "best before" date on the specification or label, assuming proper storage. Use it as a guide, record it, and trust your observations over the date when they disagree.
Storage that works
- Cold: a dedicated refrigerator for sensitive materials (never one used for food), and a cool room for the rest.
- Dark: amber or opaque glass, in closed cabinets.
- Full: decant into smaller bottles as stock is used, so there is little air above the liquid.
- Sealed: caps with good liners, closed promptly.
- Inert gas: some labs blanket sensitive materials with nitrogen or argon before closing.
- Labeled: name, code, lot, date received, date opened.
Some materials solidify or crystallize in the cold. Let them return to room temperature and become fully liquid and homogeneous before weighing. Flammable materials and alcohol need storage appropriate to their hazard — see perfume lab safety basics.
Checking a material before use
- Check the dates on the label against your records and any supplier shelf life.
- Look at it: color changes, cloudiness, crystals or separation.
- Smell it in dilution beside a retained reference sample or your recorded description. Oxidized citrus often smells flat, harsh or turpentine-like.
- If it has changed, decide and record: use, use with adjustment in trials only, or discard.
Why oxidation is also a safety issue
Oxidation of some fragrance components produces substances that are more potent skin sensitizers than the original materials — a well-documented effect for terpenes such as limonene and linalool. That is one reason some IFRA Standards set specifications, such as limits on peroxide levels or requirements for antioxidants, for certain materials. Using fresh, well-stored materials is part of making a safe product, not only a good-smelling one. The IFRA Standards guide explains specifications.
Recording dates
A material record without dates cannot tell you what is still usable. Record the date received and lot for every delivery, the date opened, and a review date. When you count stock, check dates as well — the counting habit described in fragrance raw material inventory is a natural moment to do it. Differences between kinds of natural material, which affect how they age, are covered in essential oils, absolutes, resinoids and isolates. For the full material record, see the raw material documentation guide.
Frequently asked questions
How long do essential oils last?
It varies widely: expressed citrus oils may change noticeably within a year or two of opening even when stored well, while some woody and resinous oils keep for many years. Follow the supplier's guidance and check by smell.
Should I add an antioxidant to materials?
Some suppliers add antioxidants to sensitive materials. Adding your own is a formulation decision with consequences for the finished product; record it and include it in your safety documentation.
Written and reviewed by the RUŌOD Lab team. This article is general education about perfume formulation and record-keeping; it is not legal, regulatory or safety advice, and the examples are illustrations, not validated commercial formulas. How we write and check these guides.