Trust matters more in skincare than in most categories, because people make real decisions about their skin based on what a tool tells them. So here is exactly how Fungalscan decides whether an ingredient is safe, caution, or avoid for fungal-acne-prone skin. Nothing here is a black box.

The core rule

Malassezia, the yeast behind fungal acne, is lipid-dependent: it cannot synthesize its own fatty acids and instead harvests them from its surroundings. The dermatology and cosmetic-chemistry literature indicates it readily uses fatty acids in roughly the C11 to C24 carbon-chain range. That single mechanism is the backbone of every verdict:

  • An ingredient that can supply usable fatty acids in that range leans avoid.
  • An ingredient that cannot leans safe.
  • An ingredient where availability is genuinely unclear is marked caution.

The three factors we weigh

1. Chemical family. We start by identifying what the ingredient is: a free fatty acid, a plant oil, a fatty alcohol, an ester, a polysorbate, a fatty-acid peptide, or something unrelated to fatty acids. Family sets the starting hypothesis.

2. Carbon-chain length. Family is not destiny. The concern is the C11 to C24 window, so a medium-chain ingredient such as caprylic/capric triglyceride can be safe while a long-chain triglyceride is not. We look at the actual chain length the ingredient delivers.

3. Ethoxylation. Heavy PEG-ylation reduces how available a fatty acid is to the yeast. This is why we clear ingredients like PEG-40 Hydrogenated Castor Oil that “PEG = bad” rule-based scanners wrongly flag. We read the chemistry, not the prefix.

Where simpler tools go wrong

Two patterns separate a fungal-acne-specific assessment from a generic “clean beauty” score:

  • The peptide blind spot. Fatty-acid peptides (palmitoyl, stearoyl, myristoyl, lauroyl) are a peptide with a fatty-acid tail. Generic scanners rate them as gentle hydrators and miss that the tail is malassezia food. We flag them.
  • The PEG false alarm. Rule-based tools flag every PEG ester. We assess whether ethoxylation has actually defused the fatty acid, and often clear them.

The genuinely contested calls

A few ingredients are not clear-cut, and we would rather explain the disagreement than pretend it away.

  • Cetearyl alcohol. Some references list the fatty alcohols (cetyl, stearyl, cetearyl) as triggers, and some people report tolerating them fine. The fatty-acid backbone sits in the problem range, so we lean toward flagging them, though reactions vary more here than with, say, coconut oil. This is a common reason our verdict differs from a blanket “alcohols are fine” or “alcohols are bad” tool.
  • Polysorbate 80. It is a sorbitan fatty-acid ester, which is why we treat it as a trigger, yet it usually sits low on the ingredient list at small amounts and many people tolerate it. Generic scanners that score broad ingredient safety often pass it without noting the fungal-acne angle at all.

When the evidence is split like this, we use a caution verdict rather than forcing a confident answer.

Sources

We ground verdicts in two layers of evidence:

  • Primary literature on malassezia’s lipid metabolism and fatty-acid utilization from dermatology and microbiology research.
  • Established community references that have aggregated and field-tested that research against real products over years, which is valuable precisely because fungal acne is under-studied relative to how common it is.

When these disagree, or when an ingredient is novel and poorly characterized, we default to caution.

How we handle uncertainty and updates

We treat verdicts as living, not fixed. When new evidence emerges, formulations change, or an ingredient turns out to be more or less available than assumed, we revise. If you think a verdict is wrong, you can tell us through the support page with the exact INCI name and your reasoning, and we review every flag against sources before changing it.

The honest limits

Three things this method cannot do, and we will not pretend otherwise:

  1. It is not a diagnosis. We screen ingredients; we do not diagnose your skin. See a clinician.
  2. It cannot account for your individual tolerance. Two people can react differently to the same “caution” ingredient.
  3. It depends on an accurate label. If a product’s printed ingredients are wrong, outdated, or misread, the verdict inherits that error.

That is the whole method. For the ingredient families it produces, see the trigger list, and for the big picture, the complete fungal acne guide.