An ingredient list on a cosmetic product is written under one body of law. In Korea that is the Cosmetics Act, administered by the Ministry of Food and Drug Safety. But many of those same substances are also registered under a second body of law, the Act on the Registration and Evaluation of Chemical Substances, known as K-REACH and administered by the Ministry of Environment.
The two systems ask different questions. Cosmetics regulation asks whether a substance is safe on skin at a given concentration in a given product type. Chemical regulation asks whether a substance is hazardous to handle, whether it persists in the environment, whether a facility storing it needs an emergency plan.
We hold both datasets. We matched them on CAS number to see how often the two systems land on the same substance, and how often they disagree.
The overlap
Of 21,796 cosmetic ingredients in our database, 8,403 carry a CAS number. Of 47,041 substances in our K-REACH database, 41,674 carry one. Matching on exact CAS produces 3,128 shared identifiers, covering 3,997 cosmetic ingredient records and 3,129 chemical substance records.
That is 48 percent of the cosmetic ingredients we hold a CAS number for. Roughly half the identifiable cosmetic ingredient universe is also a registered chemical.
Sorting the overlap by whether each system flags the substance gives four groups.
| K-REACH flags it | K-REACH does not | |
|---|---|---|
| Cosmetics regulation restricts or prohibits it | 90 | 587 |
| Cosmetics regulation does not | 80 | 2,371 |
The bottom-left cell is the one worth looking at. Eighty substances carry no cosmetic restriction in any of the 10 markets we track, and are simultaneously flagged under Korean chemical law.
What sits in that cell
The most recognizable entries are pH adjusters.
| Ingredient | Listed cosmetic function | K-REACH designation | GHS |
|---|---|---|---|
| Sulfuric Acid | pH adjuster | Toxic, priority control, accident preparedness, registration required | Danger. Corrosive to metals, skin corrosion 1, acute inhalation toxicity 2 |
| Hydrochloric Acid | pH adjuster | Toxic, accident preparedness, registration required | Danger. Compressed gas, acute oral 3, skin corrosion 1A, acute inhalation 3 |
| Nitric Acid | pH adjuster, solvent | Toxic, accident preparedness, registration required | Danger. Oxidizing liquid 1, skin corrosion 1, acute inhalation 1 above 70 percent |
| Hydrobromic Acid | pH adjuster | Toxic, registration required | Danger. Compressed gas 2, skin corrosion 1A, acute inhalation 3 |
There is nothing contradictory here once the question each system is asking becomes clear. A cosmetic formula that uses sulfuric acid to bring pH into range contains a trace amount, fully neutralized in the finished product. The Cosmetics Act sees no reason to set a limit. The chemical legislation is not looking at the finished cream. It is looking at the drum in the warehouse, and a drum of sulfuric acid needs an emergency response plan whether it is destined for a cosmetics plant or a steel mill.
The second cluster is different. Here the two systems are not looking at separate objects. They are looking at the same one and dividing it up differently.
Fourteen ingredient records in our cosmetic database are nonoxynols, listed as emulsifying surfactants: Nonoxynol-1, Nonoxynol-8, Nonoxynol-10 and related entries at CAS 9016-45-9, 27177-05-5, 37205-87-1, 68412-54-4 and 26027-38-3. None carries a cosmetic restriction in our data.
In K-REACH those same CAS numbers resolve to a single group, nonylphenol ethoxylates, designated as toxic and restricted, with GHS classifications for reproductive toxicity category 2 and aquatic chronic toxicity category 1. The chemical system treats them as one regulated family. The cosmetic system lists them as fourteen separate ingredients with no restriction attached.
A handful of others in the same cell:
| Ingredient | Cosmetic function | K-REACH designation |
|---|---|---|
| Isophorone Diisocyanate | Film former | Toxic, priority control, accident preparedness, registration required |
| m-Cresol | Fragrance | Toxic, accident preparedness, registration required |
| p-Cresol | Fragrance | Toxic, registration required |
| Didecyldimonium Chloride | Antistatic, hair conditioning | Toxic, registration required |
| Sodium Hypochlorite | Oxidizing agent | Toxic, registration required |
| Chlorine Dioxide | Deodorant agent | Toxic, accident preparedness |
| Triphenyl Phosphate | Plasticizer | Toxic, registration required |
The reverse case, 587 substances restricted as cosmetic ingredients that carry no chemical designation at all, we have looked at separately.
The silicones, revisited
We wrote recently about cyclotetrasiloxane, cyclopentasiloxane and cyclohexasiloxane, three ring sizes of the same structure. Under cosmetics regulation, D4 is prohibited in the EU and ASEAN in our data, while D5 and D6 carry nothing. Same function, same chemical family, different treatment.
Running the same three CAS numbers against K-REACH inverts the picture.
| Cosmetics regulation | K-REACH | |
|---|---|---|
| D4, CAS 556-67-2 | Prohibited in EU and ASEAN | Toxic, priority control. PBT and vPvB under Ministry of Environment Notice 2022-79, Appendix 665. GHS: flammable liquid 3, reproductive toxicity 2, aquatic chronic 1 |
| D5, CAS 541-02-6 | No entry | Priority control. PBT and vPvB under the same notice, Appendix 664 |
| D6, CAS 540-97-6 | No entry | Priority control. PBT and vPvB under the same notice, Appendix 663 |
The three appear in the same notice at consecutive appendix numbers, 663, 664 and 665. The chemical regulator evaluated them as a set for persistence and bioaccumulation and reached the same conclusion for all three. The cosmetics regulator evaluated D4 on its own hazard profile and left the other two alone.
Neither is inconsistent. Persistence in the environment and safety on skin are different properties, and a substance can rate badly on one while raising no concern on the other. But an ingredient list that shows cyclopentasiloxane and nothing else is telling you about only one of those two assessments.
D4 carries a further Korean designation added in 2025, listed as a substance hazardous to human health and the environment with an ecological hazard content of 25 percent, under National Institute of Chemical Safety Notice 2025-19. Our records show CAS 293-51-6, a second identifier used for D4 in cosmetic listings, has no K-REACH entry at all.
What these figures do and do not say
A K-REACH flag is not a cosmetic safety warning. The designations in this analysis are about industrial handling, storage, environmental persistence and worker exposure. Sulfuric acid appearing on an accident preparedness list says nothing about whether a pH-adjusted toner is safe to use. Reading chemical designations as consumer safety signals produces the ingredient panic that better data is supposed to prevent.
Absence of a flag is not clearance either. The 587 substances that carry a cosmetic restriction but no K-REACH flag are led by colorants and citrus extracts. They are absent from the nine chemical designation lists we track, but 576 of them do appear in the existing chemical inventory. Not being on a hazard list is not the same as not being registered.
These figures are a floor, not a total. Matching required an exact CAS string on both sides. Our cosmetic data contains 34 records where the CAS number has a formatting fault, an extra zero padded into the final segment, which we traced to a source data issue. Correcting those adds 17 matches. We have left the raw figures as they are and flagged the gap rather than adjusting the number.
One CAS is not always one substance. Fourteen cosmetic ingredient records map to five nonoxynol CAS numbers, which map to one K-REACH group. Counting ingredients, CAS numbers or chemical substances gives three different answers to the question of how large the overlap is. We have given all three: 3,128 shared CAS numbers, 3,997 cosmetic ingredient records, 3,129 chemical substance records.
Methodology and sources
Cosmetic ingredient data comes from the Korea Cosmetic Association ingredient dictionary. Cosmetic regulatory entries are compiled from Korea's Ministry of Food and Drug Safety open data and EU CosIng Annexes, covering 10 markets. Chemical substance data comes from Korea's public data portal, covering K-REACH substance registrations and GHS classifications published by the Ministry of Environment and the National Institute of Chemical Safety.
Matching was done on CAS number with exact string comparison after splitting multi-value fields. Cosmetic records separate multiple CAS numbers with a comma and space. Chemical records use commas, slashes or ampersands inconsistently across 18 rows. No value was altered to force a match.
Cosmetic figures reflect our database as of August 2026: 21,796 ingredients, 31,191 regulatory entries across 10 markets. Chemical figures reflect 47,041 substances and 50,052 regulatory entries as of the same date.
Regulatory data changes. Verify against the current official source before relying on any of this for a compliance decision.
For the underlying data, see K-Beauty Cosmetic Ingredients and K-REACH Chemical Substance on RapidAPI.
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