Essential storage keeps sign-in, your bag and requested features working. With your permission, optional analytics, sampled session replay, error reports and affiliate tools help us understand and improve the site.
You can use the site without optional tracking and change your choice from the footer. Read the cookie details.
Paste any product's ingredient list. We flag the fatty acids, esters, polysorbates and yeast ferments reported to feed Malassezia — and the classes that don't. It over-flags by nature (the science is in-vitro), so treat flags as a shortlist to patch-test, not a sentence.
Malassezia is a lipid-dependent yeast — the founding lab study (Wilde & Stewart, 1968) found it won't grow unless fatty acids longer than about C10 are present, and a 2025 study testing individual fatty acids up to C24 confirmed growth across that window, though very unevenly: palmitic acid (C16) and oleic acid supported the most efficient growth while several others (myristic, arachidic, behenic, lignoceric) only supported weak, limited growth. So 'C11–C24' is a reasonable summary of the tested range, not a claim that every fatty acid in it feeds the yeast equally well — oleic and palmitic are the best-evidenced triggers; several others are flagged mainly for being in the same structural family. Separately, Malassezia's own lipases release oleic acid from sebum, and free oleic acid has been shown to disrupt keratinocyte differentiation and trigger inflammation — a real mechanism, though it describes what the yeast does to sebum rather than a direct test of each cosmetic ingredient on skin.
The polysorbate emulsifiers are fatty-acid esters of sorbitan (polysorbate 20/40/60/80 ≈ lauric/palmitic/stearic/oleic) and have been shown to support Malassezia growth in vitro, which is why fungal-acne lists flag them. They appear in both rinse-off and leave-on products (as solubilisers), usually far below lab-assay levels, so real-world tolerance varies.
A patch-test caution, not a hard avoid. A 1995 lab study found Malassezia furfur really does hydrolyse synthetic fatty-acid esters back into free fatty acids — ethyl esters (like ethyl oleate) fastest, isopropyl esters (isopropyl palmitate, isopropyl myristate) next — and the released unsaturated fatty acids fed the yeast's growth more than saturated ones did. So the mechanism is real for at least some esters. But this remains the biggest over-flagging bucket: many ubiquitous emulsifiers (glyceryl stearate, PEG-100 stearate) are built so the fatty acid isn't released in a usable form, and many fungal-acne-prone people tolerate them fine, especially in rinse-off. Treat a match as 'worth patch-testing', not 'certainly breaks you out'.
Sorbitan fatty-acid esters (the non-ethoxylated cousins of polysorbates — same fatty-acid-plus-sorbitan backbone, without the polyoxyethylene chains) are flagged by analogy, not by direct evidence: polysorbates (Tweens) are a well-documented Malassezia growth substrate used in classic mycology to tell species apart, but no study we could find has tested plain sorbitan esters (Span-type) the same way. Since the fatty-acid ester bond a lipase would need to hydrolyse is chemically the same in both, it's a reasonable inference that sorbitan esters behave similarly — but it is an inference, not a direct finding. Treat this as a soft, analogy-based patch-test flag rather than an evidenced trigger.
A precautionary, community-driven caution — not a proven trigger. People managing fungal acne often avoid fungal/yeast ferments like Galactomyces on the theory that a yeast-derived ingredient might feed Malassezia, but direct evidence it worsens fungal acne is essentially absent. The mechanism often cited — that Galactomyces activates the aryl-hydrocarbon receptor (AhR) — actually points the other way: Galactomyces-ferment AhR activation is documented as skin-barrier-protective and anti-inflammatory (it restores filaggrin), not a driver of disease. We keep it a soft caution only because it is a live-yeast-derived ferment some people report reacting to. Note: bacterial ferments (Lactobacillus, Bifidobacterium) are NOT in this group and are generally fine.
Worth separating from its stable cousin squalane. Squalene is unsaturated and oxidises readily on skin into squalene monohydroperoxide, which is comedogenic — more so than several well-known comedogenic cosmetic ingredients. A 2023 study found Malassezia restricta itself drives this oxidation on skin, producing squalene monohydroperoxide that alters the skin barrier — so the yeast and squalene oxidation are mechanistically linked. Squalane (the saturated, hydrogenated form) has none of this — no double bonds to oxidise — and stays generally fine; squalene is the one to patch-test.
Chemistry gives a clear reason these shouldn't feed Malassezia: mineral oil and petrolatum are saturated hydrocarbons with no ester bond for a lipase to hydrolyse and no fatty acid to release; silicones (dimethicone, cyclomethicone) aren't lipids in the sense the yeast metabolises; squalane's saturated backbone has no double bonds to oxidise the way squalene does. Malassezia is a lipid-dependent yeast that grows on specific fatty acids, so ingredients carrying no usable fatty acid fall outside what it can metabolise. This is reasoned from that chemistry rather than a dedicated study of each ingredient — a thinner evidence base than the flagged ingredients above, but a well-founded one.
Caprylic/capric triglyceride (MCT) is built from C8 and C10 fatty acids — both at or below the chain length Malassezia needs to grow at all, per the foundational 1968 study (fatty acids must be longer than C10). Glycerin and propanediol are a different case entirely: they're simple humectant polyols, not fatty acids or fatty-acid esters, so there's no lipid for Malassezia's lipases to act on in the first place. Generally well-tolerated on fungal-acne-prone skin.
We match each ingredient against classes reported to feed Malassezia (fungal acne): free fatty acids in the ~C11–C24 range, esters that hydrolyse back into them, polysorbate and sorbitan emulsifiers, and fungal (yeast) ferments — plus a short list of classes that are NOT a food source (inert hydrocarbons, silicones, short C8–C10 lipids, simple humectants). The trigger classes come from the derm literature summarised by Gaitanis et al. and the reference list SkinSort's checker cites. Matching is literal substring matching on ingredient names.
Read this as a screen, not a verdict. The entire trigger list rests on IN-VITRO (lab-dish) studies of which lipids Malassezia can metabolise — that is not the same as a study showing these ingredients cause breakouts on real skin, and growth in those studies was strongly concentration-dependent (some fatty acids fed the yeast at low doses but killed it at higher ones). So this checker OVER-FLAGS: it catches ubiquitous, usually-harmless emulsifiers and thickeners (glyceryl stearate, PEG-100 stearate, polysorbates) that many fungal-acne-prone people tolerate perfectly well, especially in rinse-off products. Malassezia also lives on nearly everyone's skin; an ingredient 'feeding' it in a dish does not mean it will flare you. Use flags to shortlist things to patch-test, not to fear.
Last verified July 2026. Citations and regulatory status (FDA rulings, EU bans, retracted studies) can change over time — every source link on this page is checked weekly for dead or moved URLs, and this lens is re-audited on its underlying evidence at least once a year. See our full bibliography →