How we grade the evidence
Every claim we publish carries a letter grade. The grade is not our opinion of a product, it is a measure of how much credible human evidence supports the underlying claim, and how likely that evidence is to hold as more studies arrive. This page is the fixed rubric we apply. We publish it so you can check our reasoning, not take it on faith.
What raises and lowers a grade
- Randomized, controlled, and blinded
- Replication by independent labs
- Clinically real endpoints (hair count, weight)
- Pre-registered protocols
- Effect sizes that survive meta-analysis
- Manufacturer-funded with no independent check
- Surrogate endpoints standing in for outcomes
- Tiny samples, high dropout
- Results that fail to replicate
- "Clinically proven" with no published trial
Our review process
We do not sell advertising to ingredient or product manufacturers, and no grade is ever influenced by a commercial relationship.
Where a company we have written about also makes a product we mention, we disclose it in that specific article. The publication is reader-supported. If that ever changes, this page changes first, and you will see it in the revision log.
Grades for hair treatments change. Know when they do. Get an alert when a grade moves, plus each new review. About 2 emails a month. No products, no sponsors.