Benefits of Diaminopyrimidine Oxide in Hair Care

Diaminopyrimidine oxide is a synthetic pyrimidine derivative used as a hair care raw material, not as a pharmaceutical ingredient. In the European Union its use is capped at 1.5% in hair products. This page sets out its identity data, the regulatory position in each main market, what published studies reported, and what to request for diaminopyrimidine oxide powder.

What Diaminopyrimidine Oxide Is, and What It Is Not

Diaminopyrimidine oxide is one substance with one CAS number, and it is routinely confused with a different molecule whose name contains the same words.

Chemical identity and CAS number

Two identifiers settle what the material is: the name Diaminopyrimidine Oxide and CAS 74638-76-9. EU cosmetics law lists the substance under both a common and a systematic name, and those are the values a buyer should match against the supplier's documents.

Trade names and the pyrrolidinyl analogue

Supplier catalogues and the studies in the Sources list below give this substance, CAS 74638-76-9, under the name Kopexil; the two names identify one material. A genuine second substance is easy to mistake for it, because pyrrolidinyl diaminopyrimidine oxide shares most of its name while being a different molecule.

Regulatory Limits and Status by Market

Only the European Union publishes a numeric limit for this material, and that number is 1.5%.

• European Union: EU Annex III entry 93

EU Annex III entry 93 of Regulation (EC) No 1223/2009 names diaminopyrimidine oxide, records its CAS number, restricts it to hair products, and sets a maximum concentration of 1.5%. It draws no leave-on or rinse-off distinction, so formulators should confirm how the entry applies to their category. Commercially, that is the most useful fact here: as a cosmetic active ingredient, diaminopyrimidine oxide in hair care can reach the EU market under an existing entry, without a novel-substance route.

• United States: permitted in cosmetics, not an approved drug

The 2024 study cited below records that FDA has not approved diaminopyrimidine oxide as a drug. In the United States, whether a hair product is a drug or a cosmetic turns on the claim rather than the ingredient, and a hair-regrowth claim falls on the drug side of that line. Claim wording should be agreed with the brand's regulatory adviser before artwork is signed off.

• Other markets: what to confirm

This review found no comparable published numeric limit for Canada, Japan, Korea or China, so buyers should obtain the current position locally. Claim categories, not only concentration limits, decide what may be said on pack, so confirm the claim route alongside the limit before labelling.

What Published Studies Reported, and Where They Disagree

The evidence cited for this material comes from three kinds of study, and the weight they carry is not the same.

• Mechanisms described in the literature

Reviews describe proposed mechanisms rather than one settled pathway. Jalilzadeh and colleagues summarise earlier work as showing that the substance softens hair follicles and enhances blood vessel dilation, inhibits peripilar fibrosis by suppressing lysyl hydroxylase activity, and extends the anagen growth phase through follicular keratinocytes.

• Human studies: what was measured

The larger, published in Dermatologic Therapy in 2021, assessed a five-ingredient finished formula combining the substance with arginine, SP94, piroctone olamine and Vichy mineralizing water. Investigators enrolled 527 subjects with mild androgenetic alopecia, of whom 357 were evaluable, and reported after three months of once-daily use that hair loss was reduced in 89.0% of subjects, higher in women at 92.5% than in men at 83.8%, with satisfaction of 7.9 out of ten and tolerance rated good to very good by 98.6%.

• What limits apply to those results

Three limits belong beside those numbers. The study was open-label with no control group, so expectation effects cannot be separated from product effect. The formula contained five ingredients, so the result cannot be attributed to this substance alone. Several authors declared consultancy or employment with the finished-product company. A second dataset, summarised in the same literature, compared a 1.5% topical solution against placebo in 351 patients and reported a fall in telogen hair and a rise in anagen hair in the treated group, although that figure comes from a secondary summary rather than the original paper.

• The mouse comparison favouring this material

A widely cited mouse study in Bioimpacts (2024) compared a 5% hydro-alcoholic solution against minoxidil in 27 C57BL/6 mice over 28 days. The authors reported greater hair weight, follicle count, anagen percentage and overall hair growth than the minoxidil group, higher expression of the growth factors HGF and VEGF, and no statistically significant differences in liver or kidney weights or tissue morphology. Their stated conclusion was that the 5% solution proved an effective hair growth stimulator.

• The counterweight, and the evidence gap

The same group's later paper supplies the counterweight: an earlier rat study by Orasan and colleagues found minoxidil slightly more effective, and the authors state that variation across dosage, formulation, model and duration is why standardised head-to-head clinical trials are still needed. A further comparison they summarise tested a 1% niosomal preparation against 2% niosomal minoxidil over six months in men with androgenetic alopecia and reported greater hair-loss reduction in the first group, although concentrations were not matched.

• The in-press stability and skin-permeation study

A 2025 manuscript accepted by Pharmaceutical Sciences characterised the material by DSC, FTIR, UV-Vis and HPLC and stored 0.5%, 1% and 2% formulations for six months at 4, 25 and 40 degrees C under ICH conditions. The authors reported t90 values of 39 to 50 months for this substance against 20 to 42 months for minoxidil, with zero-order degradation. Permeation was measured using Franz diffusion cells on full-thickness mouse skin, where they reported a higher permeation rate than minoxidil. The work is in press and in vitro on animal skin.

• Why regulatory status is not a safety comparison

Minoxidil is an approved drug in the United States and the European Union; diaminopyrimidine oxide is not approved as a drug in either market. The two sit in different frameworks with different evidence requirements, so their safety databases are not directly comparable. Nothing here should be read as a comparative safety conclusion, and any safety assessment should rest on the buyer's own toxicological data package.

Formulation and Sourcing Notes for Buyers

For diaminopyrimidine oxide in hair care formulations, the binding constraint on diaminopyrimidine oxide powder is the EU ceiling rather than the maximum figure on a supplier datasheet.

• Addition levels and the 1.5% ceiling

Within the European Union, Annex III entry 93 sets 1.5% in hair products as the ceiling in the ready-to-use preparation, and that applies whatever a supplier's recommended range states; working levels of diaminopyrimidine oxide powder below it depend on the base, the claim category and the rest of the active system. Formulators outside the EU should still confirm the position locally, because claim categories as much as concentration limits govern what may be said on pack.

• Batch documents and the goods-in check

A purity figure alone is not a purchase basis. The documents worth requesting per batch are the certificate of analysis, the HPLC purity result, heavy-metal and residual-solvent reports, microbiology results and the batch-matching safety data sheet. Because the pyrrolidinyl analogue and this material are both white crystalline powders bought for diaminopyrimidine oxide in hair care applications, the fastest goods-in control is to match three values against the certificate: CAS number, molecular weight and HPLC retention time. A supplier selling cosmetic raw material on a specification sheet alone leaves that check to the buyer.

• Storage, shelf life and packaging

The diaminopyrimidine oxide powder should be held at 15 to 25 degrees C in an airtight container, protected from light and moisture, over a stated shelf life of 24 months. It ships as 1 kg aluminium foil bags and 25 kg fibre drums, with a minimum order of 1 kg and samples available.

Frequently Asked Questions

For specification sheets, batch documentation or samples of diaminopyrimidine oxide powder for diaminopyrimidine oxide in hair care projects, contact our technical team.

Sources

1. European Commission. Regulation (EC) No 1223/2009 on cosmetic products, Annex III, entry 93 (Diaminopyrimidine oxide, CAS 74638-76-9). eur-lex.europa.eu
2. Reygagne P, Mandel VD, Delva C, et al. An anti-hair loss treatment in the management of mild androgenetic alopecia: results from a large, international observational study. Dermatologic Therapy. 2021;34(6):e15134. pubmed.ncbi.nlm.nih.gov/34532936
3. Jalilzadeh S, Hamishehkar H, Monajjemzadeh F. Kopexil vs minoxidil: in vivo comparative study on hair growth, hair growth promoting factors and toxicity. Bioimpacts. 2024;15:30484. pmc.ncbi.nlm.nih.gov/articles/PMC12008251
4. Jalilzadeh S, Hamishehkar H, Monajjemzadeh F. Kopexil vs minoxidil: exploring the physicochemical characteristics, storage stability and skin permeability. Pharmaceutical Sciences. In press. ps.tbzmed.ac.ir/Inpress/ps-43014.pdf