Source: Skin Aqua Super UV Moisture Milk SPF50+ PA++++
Product: スキンアクア スーパーモイスチャーミルク (40 mL)
Manufacturer: Rohto Mentholatum Co. (ロート製薬), Japan
Label: SPF50+ / PA++++ / Super Waterproof
Preset key: skinaqua
Sources for the ingredient list
The verified ingredient list comes from Japanese-language regulatory and retail sources, cross-checked across:
- ロート製薬公式商品ページ (Rohto official)
- @cosme product page
- Cosmetic Info Japan database (10125561)
- Amazon Japan listing (B01MRBST6H)
Active ingredients (UV filters + photostabilizer)
The Japanese full-ingredient list (全成分) for the standard SPF50+ PA++++ Super Moisture Milk shows three primary UV filters plus one photostabilizer. Ingredients in Japanese law are listed in decreasing order of concentration for items above 1%, with sub-1% ingredients allowed in any order at the end of the list — so the early-list position of zinc oxide is informative, while the relative ordering of DHHB and the photostabilizer is less reliable.
| INCI / common name | Japanese name | Position in list | Inferred % |
|---|---|---|---|
| Zinc Oxide | 酸化亜鉛 | #1 (first ingredient) | ~10% |
| Ethylhexyl Methoxycinnamate (Octinoxate) | メトキシケイヒ酸エチルヘキシル | mid-list, before "1% line" | ~7.5% |
| Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB / Uvinul A Plus) | ジエチルアミノヒドロキシベンゾイル安息香酸ヘキシル | post-1% region | ~3% |
| Bis-Ethylhexyl Hydroxydimethoxybenzylmalonate (DESM / Oxynex ST) | マロン酸ビスエチルヘキシルヒドロキシジメトキシベンジル | post-1% region | ~1% |
No iron oxides. No titanium dioxide. An earlier draft of this preset incorrectly included those based on a stale incidecoder listing (which appears to have been from a different SKU or formulation revision). The Japanese ingredient list is the authoritative reference.
Concentration inference reasoning
Japanese regulatory caps relevant to this formulation:
- Octinoxate: up to 20% in Japan (vs FDA 7.5%, EU 10%). Position in list (after the 1% line markers like phenoxyethanol/methylparaben) suggests a single-digit %, consistent with the "rough" 7.5% I've used.
- Zinc Oxide: up to 25% in Japan. Position #1 in the list places it at the highest concentration, but its mass density (5.6 g/cm³) means even moderate w/w percentages dominate by weight. ~10% is typical for hybrid milk-type formulations and consistent with SPF50+ performance.
- DHHB: up to 10% in Japan/EU. Position after octinoxate suggests lower concentration, ~2–4%. Used 3%.
DESM (bis-ethylhexyl hydroxydimethoxybenzylmalonate, marketed by Merck as Oxynex ST) is a photostabilizer with weak intrinsic UV absorption — it primarily quenches triplet states of avobenzone-class chromophores via TTET. Not modelled as a primary filter in the atlas; not included in the preset. Typical use level 0.5–2%.
Predicted SPF (atlas model)
Using the recalibrated f(c) for ZnO and the default organic f(c):
| Mode | Predicted SPF | Predicted UVA-PF | Critical λ | HEV blockade |
|---|---|---|---|---|
| Lab (2 mg/cm²) | 100+ (ceiling) | 50+ | 376–380 nm | ~5–10% |
| Real-world (0.75 mg/cm²) | ~50–55 | ~25–35 | same | same |
The label is SPF 50+ PA++++ (UVA-PF ≥ 16). Real-world prediction at 0.75 mg/cm² lands at SPF 52 — close to the labeled value. PA++++ requires UVA-PF ≥ 16; the 3% DHHB + 10% ZnO combination clears this comfortably in the lab regime.
The atlas model's "100+" lab ceiling is consistent with how SPF testing actually works — products formulated for SPF 50+ (the FDA cap) are typically in-vitro SPF 80–150, capped at "50+" on the label by regulation rather than by physical limit.
Why this formulation works (qualitatively)
- Zinc Oxide carries broad UVB+UVA-2+UVA-1-to-370 nm coverage at 10% w/w, with sharp Tauc edge at 368 nm
- Octinoxate adds a strong UVB peak at 308–311 nm (where ZnO is already covering, but octinoxate's molar attenuation per gram is higher)
- DHHB fills the UVA-1 gap from 340–400 nm where ZnO drops off, peaking at 354 nm
- DESM/Oxynex ST keeps the system photostable — octinoxate is photolabile in the absence of stabilizers, and DESM also serves as a singlet-oxygen quencher
Together this is a textbook Japanese hybrid formulation: enough UVB from octinoxate to keep the SPF integral high, enough UVA-1 from DHHB for PA++++, with ZnO providing the broad-spectrum backbone and DESM keeping it photostable across product shelf life.
Caveats
- INCI ordering is informative but not a precise concentration measurement; my inferred percentages are within ~30% of likely real values.
- The product has multiple SKUs and formulations — the atlas preset corresponds to the Super Moisture Milk SPF50+ PA++++ (40 mL, super waterproof), not the older PA+++ version or the gel/tone-up SKUs in the same product family.
- Rohto/Mentholatum reformulates periodically; this corresponds to the post-2017 specification verified above. Newer revisions may differ.
Files referenced
MASTER-SYNTHESIS.md— atlas-wide synthesis with regulatory matrixresearch/uva-organic/claims/c003-dhhb.md— DHHB primary photochemistryresearch/inorganic/claims/c001-zinc-oxide.md— ZnO physical chemistryresearch/uvb-organic/claims/c001-octinoxate.md— Octinoxate spectrum + photodegradationresearch/photostab/claims/c007-desm-oxynex-st.md— DESM mechanismresearch/calibration/zno-deep-dive.md— ZnO calibration (peak E1% 160 vs prior 9800)