A randomised controlled trial (RCT) compares people given a treatment with people given a placebo or another treatment, chosen by chance, so it gives stronger evidence than a small study with no comparison group. When we cite research on an ingredient, we say what kind of study it was, and that studies on an ingredient are not proof that a particular product works for you.
Stronger evidence
Large RCTs, ideally double-blind, and reviews that pool several trials.
Weaker evidence
Small open studies, lab or animal studies, and before-and-after photos without a control group.
Questions to ask
How many people? Was there a placebo? How long? Who paid for it? Was it the same product or just one ingredient?
Questions
Are lab studies useless?
No, they suggest ideas, but they don't show what happens on a real scalp.
Why do you cite ingredient studies?
To explain why an ingredient was chosen, while being clear they are not product proof.