What it is
The register’s chemical name for it: “L-2-Pyrrolidone-5-carboxylic acid.”
- EU register name (INCI)
- PCA
- CAS number
- 98-79-3
- EC number
- 202-700-3
What the register lists it for
These are the uses the European Commission’s CosIng register lists for PCA in any cosmetic, hair roles first. They say why a maker might add it, not what it does in one formula, and they aren’t a safety rating.
- Humectant
-
Holds water in the product and on the surface it touches. Glycerin, honey and aloe are common humectants on curly-hair labels.
Register definition: “Retaining and/or preserving the moisture in a product during use.”
- Moisturizing
-
Raises the water content of the skin. Hair labels often list these for the scalp as well as the lengths.
Register definition: “Increasing the water content of the skin and keeping it soft and smooth.”
Where it sits on each label
US labels list ingredients from most to least, except that those at 1% or less may follow in any order. A name near the top is a large part of the formula. A label doesn’t mark where the 1% point falls, so further down, the order says little about how much is in it.
- Shampoos 1 label First five names: 0 of 1 Shampoos without it
- Clarifying shampoos 1 label First five names: 0 of 1 Clarifying shampoos without it
- Rinse-out conditioners 2 labels First five names: 0 of 2 Rinse-out conditioners without it
- Deep conditioners 1 label First five names: 0 of 1 Deep conditioners without it
Every label, product by product (5)
- Kristin Ess Moisture Rich Curl Shampoo Shampoo 13th of 41 names
- OLAPLEX No.4C Bond Maintenance Clarifying Shampoo Clarifying shampoo 28th of 55 names
- Cécred Hydrating Conditioner Rinse-out conditioner 22nd of 50 names
- Kristin Ess Moisture Rich Curl Conditioner Rinse-out conditioner 21st of 41 names
- Innersense Organic Beauty Hydrating Hair Mask Deep conditioner 30th of 54 names
Each line runs from the first name on a label to the last; a dot is where this ingredient sits. Makers change formulas now and then; if the list on your bottle differs, go by your bottle.
Your next step
Other humectant ingredients on these labels
- Propylene Glycol 22 labels
- Honey 19 labels
- Butylene Glycol 14 labels
- Sorbitol 11 labels
- Sodium Hyaluronate 8 labels
- Phytantriol 5 labels
- Xylitol 5 labels
- Anhydroxylitol 3 labels
Updated · The name, numbers and uses come from the European Commission’s CosIng entry (CC BY 4.0); we write the uses in US spelling and put the hair ones first. The labels are each maker’s own. The order rule is the FDA’s Cosmetics Labeling Guide. All our sources are on the Sources page.