Methodology — How DIY Cosmetica Formulates and Tests Recipes

How DIY Cosmetica formulates and tests recipes

Every recipe and every ingredient page on this site is written to the same standard: the level of detail a working cosmetic chemist would expect on a formula they were handed for the first time. This page explains exactly what that means, what we test, what we do not, and how the encyclopedia is sourced.

1. Recipe format

Every recipe on the site follows the same structure:

  • Phased ingredient table — water phase (Phase A), oil phase (Phase B), cool-down phase (Phase C), and pH-adjustment phase (Phase D) where relevant. Each ingredient is listed with its INCI name and exact percentage.
  • Percentages total 100% — never approximated, never “about.” If a recipe contains water at 52.7%, it really is 52.7%.
  • Emulsifier and preservative are explicit — the type, the amount, and the reason for choosing it. We never write “add preservative” without naming a specific one and giving its standard usage range.
  • Target pH — every emulsion and surfactant product specifies the target pH window (typically 4.5–5.5 for skin, 4.5–5.5 for hair, 9.5–10.5 for soap) and how to measure and adjust it.
  • Realistic shelf life — based on the preservative system, packaging, and storage conditions of the finished product.
  • Step-by-step method — temperatures, hold times, mixing speeds, and visual cues (e.g. “stir until the mixture turns from translucent to opaque”).
  • Make-it-yours personalisation — every recipe has a “swaps” section showing safe substitutions for different skin types and ingredient availability.

2. Ingredient encyclopedia format

Every one of the 384+ ingredient pages follows the same structure:

  • Overview — what the ingredient is, where it comes from, what grades exist, shelf life
  • What it does in a formula — the chemistry in plain English, fatty acid or active profile where relevant
  • How to use — phase, temperature, and usage percentage ranges by product type (lotions, body butters, lip balms, shampoo, etc.)
  • Best for / Worst for — which skin or hair types benefit, which should avoid
  • Common pitfalls — specific failure modes with how to prevent or fix them
  • Substitutes — concrete alternatives, not generic categories

3. What we test before publishing

  • Every recipe is made in batch and used by the formulator before publication. We do not publish theoretical recipes.
  • Patch testing is mandatory for every leave-on product before public release.
  • pH is measured with a calibrated meter (not just strips) for every emulsion and surfactant product before the recipe is locked.
  • Shelf life observation — finished products are stored under realistic conditions (a bathroom shelf, not a fridge) for at least 4 weeks before the recipe is published, watching for separation, mould, oxidation, scent drift, or pH drift.
  • Photography of every finished product, at the percentages and process times listed in the recipe.

4. What we do not do

  • We do not publish “untested” or “speculative” recipes. If a recipe is on the site, we made it.
  • We do not pad with “miracle” claims. Every functional claim is tied to a specific ingredient mechanism (occlusion, humectancy, exfoliation, antioxidation, antimicrobial, etc.) that the ingredient genuinely performs in cosmetic chemistry.
  • We do not give medical advice. Recipes are educational. For prescription-strength actives (retinoids, hydroquinone, minoxidil) we point readers to a dermatologist or doctor rather than substituting unapproved DIY versions.
  • We do not name competitor sites, suppliers, manufacturers, or other creators in published content. Ingredient information is independently sourced and rewritten — never quoted from supplier specification sheets or third-party blogs.

5. Where the ingredient information comes from

The ingredient encyclopedia is built from:

  • Published cosmetic chemistry references — Cosmetic Ingredient Review (CIR) database, INCI dictionary, peer-reviewed dermatology journals
  • IFRA fragrance and essential-oil safety standards — for maximum dermal use rates on essential oils and fragrance components
  • First-hand formulation experience — every fatty-acid profile, every melting point, every “feels tacky at high %” note has been verified in batch
  • Cross-reference between sources — when a usage range is given (e.g. “Cosgard at 0.4–1.0%”), it reflects the range agreed upon by multiple independent sources, not a single supplier’s claim

For ingredients with limited published data (newer peptides, novel actives), we say so explicitly: “Limited research — use with caution and consult a doctor before applying during pregnancy or while breastfeeding.”

6. Safety practices

  • Lye (NaOH / KOH) — always handled with goggles, long sleeves, nitrile gloves, in a ventilated space, away from pets and children. Recipes always say “add lye to water — never water to lye.”
  • Essential oils — never recommended above 1% for leave-on body products and 0.7% for scalp products. Phototoxic citrus oils are flagged with explicit warnings for sun-exposed applications.
  • Preservation — every water-containing product carries an effective broad-spectrum preservative. We do not publish “natural-only” preservation systems that we have not personally challenge-tested.
  • Pregnancy and medical conditions — flagged on every relevant ingredient page (retinoids, hydroquinone alternatives, hormone-active extracts, EGF-class peptides, papain, bromelain, salicylic acid above 2%, etc.) with a recommendation to consult a doctor or midwife.

7. Patch test guidance (always)

For every leave-on product, the recommended test before first full use:

  1. Apply a small amount to the inside of your forearm or behind the ear.
  2. Leave on for 24 hours without washing the area.
  3. Watch for redness, itching, or stinging.
  4. If any reaction occurs, do not use the product and wash the area with mild soap and water.
  5. Patch test again if the formula is updated, if you add a new active, or if you skipped patch testing on a previous batch — sensitisation can develop over time.

For scalp products, a second patch on the scalp behind the ear is recommended in addition to the forearm test.

8. How recipes are updated

When a recipe is updated (a better preservative becomes available, a new substitute is verified, a safety caveat is added), the page is edited directly and the change is timestamped in the public Git history. We do not maintain “old versions” of recipes — the current page reflects current best practice.

9. Tools we provide for free

  • Soap calculator — a free lye + water + superfat + fatty-acid calculator for cold-process soap. Includes a printable recipe sheet and full safety notes.
  • Ingredient encyclopedia — 384+ ingredients, browsable by category, with a live search and inline cross-links to every recipe that uses each ingredient.
  • Glossary — INCI quick-lookup for shopping and label-reading.
  • Community forum — open Q&A, troubleshooting, and recipe-sharing.

10. What this site is not

  • It is not a substitute for a dermatologist. If your skin reacts unexpectedly, see a doctor.
  • It is not a shop. We do not sell ingredients. Where ingredients are difficult to source we describe them generically and trust the reader to find a supplier they trust.
  • It is not a clinical-trial outfit. Our testing is on real batches in real homes, not in laboratories. Where we cite “research,” we mean published cosmetic chemistry literature, not in-house clinical trials.

If you find an error on a recipe or ingredient page, please report it on the community forum — we read every report and update affected pages.