All guides

Every guide on Patch Test, grouped by topic. Each one lists its sources at the end.

Ingredients

Hyaluronic acid, peptides, lactic acid and other AHAs, niacinamide, retinoids, hypochlorous acid: what they do, how strong they are, and how to read the label.

  1. Combining active ingredientsRetinoids, acids, vitamin C, niacinamide and benzoyl peroxide: a pairing table and a simple weekly plan.
  2. How to patch test skincareThe AAD's 7-to-10-day home test, what a reaction looks like, and how doctors test for allergies.
  3. How to read an INCI listIngredient order, the 1% line, drug facts on US sunscreens, fragrance allergens and the symbols on the back of the box.
  4. Naturium Quadruple Hyaluronic Acid Serum, decodedFour molecular weights of hyaluronic acid, read line by line, and how to layer it in a humid climate.
  5. Niacinamide explainedVitamin B3 in skincare: the trials behind it, sensible concentrations, and the vitamin C myth.
  6. Peach & Lily Power Cocktail, decodedA 10% lactic acid serum read from its label: AHA strength, pH, sensitivity and the sunscreen rule.
  7. Peptides in skincareSignal, carrier and neurotransmitter peptides: what the studies show, and why the label rarely tells you how much.
  8. Retinoids explainedThe vitamin A family, from cosmetic retinol to prescription tretinoin, and a slow start that skin can live with.
  9. Rhode skincare: what's worth knowingFour widely discussed products read from their ingredient lists: peptides, niacinamide, ceramides and what the labels show.
  10. SOS Daily Rescue spray and hypochlorous acidA three-ingredient mist built on hypochlorous acid: what the research supports, and what a spray cannot replace.

Routines by skin type

Simple routines for oily, dry, sensitive and acne-prone skin, and for living in a hot, humid tropical climate.

  1. A routine for dry skinHumectants, emollients and occlusives in plain words, and the dermatologists' habits that do most of the work.
  2. A routine for sensitive skinStinging, redness and reactions: a minimal routine, the usual suspects on labels, and when it isn't 'just sensitive'.
  3. A skincare routine by skin typeOily, dry, combination, sensitive or normal: a simple test, and a three-step routine for each type.
  4. Oily and acne-prone skinBenzoyl peroxide, salicylic acid and adapalene, used gently, with a light moisturizer and daily sunscreen.
  5. Skincare in a hot, humid climateLight textures, sweat-proof sunscreen habits, heat rash and the dry office air nobody expects in the tropics.

US and Asian skincare

How American and Asian brands differ in formulation and regulation (FDA and MoCRA, Korea's MFDS, Malaysia's NPRA), and what that means for sunscreen.

  1. Buying US beauty products from abroadHow to check a reseller, spot a counterfeit, read batch codes, and protect products from heat in transit.
  2. Cosmetics rules: US, Korea, MalaysiaWho checks a product before sale, what counts as a drug, and what a Malaysian notification number tells you.
  3. How much sunscreen to useHalf a teaspoon for the face, a shot glass for the body, every two hours: the numbers behind the advice.
  4. US and Asian skincare: two philosophiesDrug-category actives and dermatologist branding versus layering, textures and 'functional cosmetics': where the differences come from.
  5. US, European and Asian sunscreens comparedWhy a Korean SPF 50+ PA++++ and a US 'broad spectrum SPF 50' are labelled so differently, and what the filters are.

Climate and relocation

Humidity, hard water, pollution and heat: how a new city changes your skin and hair, and how to adapt your routine.

  1. Gisou's honey leave-in, decodedA honey-based leave-in read from its label, and how humectants behave in tropical humidity and dry air.
  2. Hard water and skinCalcium, soap residue and eczema: the studies behind the claims, and simple changes that don't need a plumber.
  3. Moving to a new climate: adapting your skincareHumidity, UV, water and air change when you move. A climate-by-climate plan for the first months in a new city.
  4. Pollution and skinFine particles, traffic soot, ozone and UV: what studies link to skin, and why 'anti-pollution' claims need care.
  5. Storing skincare in heat and humiditySunscreen in hot cars, vitamin C turning orange, jars in steamy bathrooms: how to keep products working in the tropics.