In short
Perfume discolors because materials change or react: vanillin and related materials can brown, indole can darken, anthranilates can yellow as Schiff bases form, phenols can react with iron, and light speeds many of these. The color itself often does not change the smell much, but it shows that something has happened, and in some products it is a commercial defect.
What you will learn
- Name the common causes of discoloration
- Trace a color change by testing lines separately
- Say when discoloration matters and when it does not
Before this lesson: Schiff Bases: Study Guide and Color Test
Common sources
| Source | Usually seen as | Notes |
|---|---|---|
| Vanillin, ethyl vanillin | Yellow to brown | Worse in soap and some bases, or under light. See the vanillin guide. |
| Indole | Pink to brown | Even small amounts in some systems |
| Anthranilates with aldehydes | Yellow, orange | See Schiff bases |
| Phenols such as eugenol | Darkening, particularly with iron | Check equipment and lids |
| Natural materials | Already colored, or deepening | Resinoids and absolutes are often dark |
| Light | Fading of added dye; color change generally | The guide on UV absorbers covers mitigation and its limits |
Does it matter?
- In a study sample: usually only as information. Record it.
- In alcoholic perfume in a clear bottle: customers may see it, and they may read it as spoilage.
- In a white cream, soap or candle: often a real problem, because the base shows the color clearly.
- As a clue: a color change may accompany an odor change. Check the smell against a fresh sample.
Tracing a change
Work out the cause with a controlled aging test:
- Note when and how the change appeared. Note the storage and packaging.
- List suspects from the table, using your functional group reading.
- In clear glass, in identical conditions, set up small samples: the full formula, the formula without each suspect, and each suspect alone in alcohol.
- Keep a set in the dark and a set in daylight, so that you can separate light from time.
- Compare against a white card at intervals, and take a photograph under the same light each time.
This is a simple version of how a laboratory would approach it, and it answers practical questions without special equipment. It takes weeks. It does not tell you what the colored species is, which would need analysis.
What you can do about it
- Remove or reduce the cause, if the formula allows. Test the effect on smell.
- Change the packaging: opaque or colored glass, tight seals.
- Choose material grades carefully, as their color and purity can differ.
- Consider stabilizers, with their limits and rules, or a colorant to hide a gradual change. Our guide on adding color covers the regulatory side, including that permitted colorants differ by market.
- Accept it, and say so. A natural perfume that darkens gradually may be acceptable to your customers. That is a decision, rather than something to be left to chance.
Practical exercise: Trace a color change
Choose one of your formulas that contains a likely source. If none does, prepare a simple test pair: vanillin in alcohol, and vanillin with a little methyl anthranilate in alcohol.
- Set up the samples as above, with a dark set and a daylight set.
- Photograph them against a white card at the start and at 2, 4 and 8 weeks.
- Note the color and smell each time, with a fresh sample as a control at the last check.
- Write which suspect or condition explains the change, and how sure you are.
You have done this well if your conclusion is based on differences between your controlled samples and states its limits.
Common mistakes
- Assuming color means spoilage. Check the smell, and the record.
- Testing only in the dark. A product in a shop is not.
- Adding dye without checking its rules. Permitted colorants are regulated.
Key terms
- Chromophore
- The part of a molecule responsible for absorbing visible light, and so for its color. New chromophores can form when materials react.
Knowledge check
Written and reviewed by the RUŌOD Lab team. This is general education, not legal, regulatory, medical or safety advice. Example dilutions and exercises are for learning, are not validated products, and have not been safety-assessed. Completing a lesson confers no qualification. How we check these lessons.