It changed color or smell

Color and odor are the attributes a customer assesses instantly and the ones a stability study lists first, because they are the visible surface of chemistry happening underneath.

The first thing anybody notices

Nobody measures the pH of a cream in their bathroom. They notice that it has gone yellow, or that it smells different from the last one. Those observations are usually correct and usually early.

What each change usually means

Yellowing or browning. Oxidation. In a vitamin C product, browning is L-ascorbic acid degrading and is a direct signal that the active is going. In an oil-rich product it is the oil phase.

Fading. Light on a natural colorant or a botanical extract.

A sharp or waxy smell. Rancidity in the oil phase.

A sour or musty smell. This is the serious one. It suggests microbial activity and it means stop, quarantine and test rather than adjust.

Fragrance fading unevenly. Components absorbing into the pack at different rates, which is a compatibility problem rather than a fragrance problem.

Natural formulas change more

Unrefined oils, botanical extracts and unbleached butters all carry their own color and smell, and all of them move. A brand built on minimally processed ingredients has chosen a product that visibly ages, and the honest position is to say so rather than to be surprised by it.

Batch-to-batch variation in the raw material adds to this: two lots of the same unrefined oil are not the same color, and a customer comparing jars will notice.

What to do about it

Decide, in advance, what range is acceptable and write it into the specification. Then tell customers what is normal, because a brand that has explained that its balm darkens slightly is in a completely different position from one receiving the question cold.

And treat smell changes differently from color changes. Color is usually cosmetic. A smell that suggests microbial activity is a different category of problem.

References