Research & Methodology

How Evi evaluates evidence.

What we read, how we weigh it, and how a rating is reached — written so you can check our reasoning, not just our conclusions.

How research is found

We start with the claim — what a product, ingredient or trend promises — and search the published literature for studies that test it, mainly through PubMed and PubMed Central.

We prefer sources anyone can open and read for free, so you can check our work. Every study we cite links to its source, with its title, journal, year and DOI where available.

What sources we consider

Systematic reviews and meta-analyses, randomised controlled trials, and other human clinical studies carry the most weight.

Narrative reviews help explain mechanisms. Lab (in vitro) and animal studies are included when they are all that exists — and we say so plainly, because a result in a dish or a mouse is not a result in people.

Brand-provided documents, press releases and social media are not treated as evidence on their own. They can point us towards published research worth reading.

Product-level vs ingredient-level evidence

Most research tests ingredients, not finished products. Evidence that an ingredient works at a certain dose does not prove a particular product — with its own concentration, formula and packaging — delivers the same result.

Every Evi rating is labelled with its scope: ingredient, product or claim. Today, most product ratings summarise the evidence for the product's key ingredients, and say so. Where a product has been studied itself, we cite that research directly.

How study quality is considered

We look at who was studied, how many people took part, whether there was a control or placebo group, how long the study ran, and whether the result has been repeated by independent researchers.

One small study can be promising. It is rarely conclusive. Consistent results across several well-designed human studies are what move a rating towards Strong.

How conflicting evidence is handled

When good studies disagree, we don't pick the one that makes the better headline. We weigh the larger, better-controlled and more recent research more heavily, and explain the disagreement in plain language.

Mixed results usually mean a more cautious rating — Promising or Limited rather than Strong.

How often reports are reviewed

Every report shows when it was published and when it was last reviewed. We revisit reports when new research is published, when a reader or brand flags something, and when a product's formula changes.

Our citation links are checked automatically every day. Broken or mismatched links are flagged for an editor to fix.

How evidence ratings are assigned

Evi uses five levels, not stars or scores. Every rating has a "Why this rating" explanation showing the reasoning and the number of sources reviewed.

Strong: Consistent results from well-designed human studies, such as controlled trials or systematic reviews.
Promising: Encouraging human research, but results are mixed, small, or not yet confirmed by larger trials.
Limited: Only a little research exists, or it comes mainly from lab, animal or very small studies.
Unsupported: The research that exists does not back the claim as it is commonly marketed.
Insufficient evidence: Evi could not find enough relevant published research to judge this yet.

Can brands pay for a better rating?

No.

Affiliate commissions, sponsorships, advertising and brand partnerships do not determine evidence ratings. Ratings are calculated from research alone — commercial data is kept out of that process entirely. A brand cannot buy a stronger rating, remove an unfavourable finding, or change what our reports conclude.

How Evi makes money

Plainly put

Affiliate commissions. Evi may earn a commission on eligible purchases made through certain retailer links. It never changes the price you pay, and every page with these links carries a disclosure.
Labelled sponsorship and advertising. Evi may offer sponsorship or advertising opportunities. Anything paid for is clearly marked Sponsored or Paid partnership, wherever it appears.
Kept separate. Commercial relationships do not determine evidence assessments, search order, trending lists or Evi Match suggestions.

Corrections & updates

When we get something wrong

If you spot an error — a misread study, a broken link, an outdated price — tell us. We review every correction request, update the report when the evidence supports it, and change its last-reviewed date.

Request a correction

Submit research

Brands, researchers and readers

Anyone can send us studies, ingredient information or documentation. We read it on the same terms as everything else. Submitting research does not guarantee coverage, or favourable coverage — it guarantees it will be considered.

Submit research as a brand Contact Evi