Ingredient Beauty BenefitsOther · Genistein
Genistein: there are two trials, and what they measured was concentration in tissue, not what the mirror shows
In two trials of 30 postmenopausal women over 24 weeks, biopsies from the skin in front of the ear showed hyaluronic acid and collagen had risen. But the comparator was estradiol and genistein lost both times, and there was no vehicle-only arm. Neither trial had an endpoint measuring anything visible.
Last checked Sep 21, 2026
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- What it is
An isoflavone found in soy. Its structure resembles oestrogen, so it is called a phytoestrogen.
- What it is used for
Products aimed at skin changes after menopause.
- How it is said to work
It is said to act weakly on oestrogen receptors in skin. That resemblance is both this ingredient's rationale and its largest unknown.
There are no numbers and no citations in this box. What has been established, and how far, is below.
At a glance
- In pregnancy
- Not established
- Irritation
- Minimal
- Daytime use
- ✓ Fine
- How well established
- Not established
- Concentration studied
- 4%
- Length of the studies
- 24 weeks
Not a measurement — reported irritation grouped into five steps. It varies between people.
“Concentration studied” and “Length of the studies” are taken straight from the research on this page. They are not a recommended dose, and the figure for each finding is written out in the text.
This is not how large the effect is but how well confirmed it is. It shows the highest grade among the findings on this page.
Genistein is an isoflavone found in soy. Its structure resembles oestrogen, so it is called a phytoestrogen, and it goes into products aimed at skin changes after menopause.
The two trials on this page have an unusual design. Unlike the other ingredients on this site, what was measured here is concentration inside a piece of skin taken from in front of the ear — how much hyaluronic acid was there, how much collagen.
Not how many wrinkles went, not how the photographs changed, not how the person felt.
That difference matters. 'Collagen in the tissue rose' and 'it looks different in the mirror' are not the same sentence. It is why this site writes the endpoint on the badge, and here that field reads 'tissue finding'.
And the comparator is estradiol. There was no vehicle-only arm. So these trials cannot say 'applying genistein makes it rise' — only 'it rose less than with estradiol'.
The two reports may be the same trial. Same group, same design, same 30 people, same 24 weeks. The abstracts do not say. We have tied them together so as not to count one trial twice.
Contents
What is established
The same ingredient at a different strength, in a different formula, is a different product. These are the conditions the studies used.
Hyaluronic acid rose — but it rose more with estradiol
A 2013 trial at the Federal University of São Paulo, prospective, randomised and double-blind.
30 postmenopausal women were divided into two groups.
- Group E — 0.01% 17β-estradiol gel, 15 people
- Group G — 4% genistein gel (isoflavones), 15 people
Applied for 24 weeks. Each participant had a preauricular skin biopsy twice — at baseline and after treatment.
What was measured is hyaluronic acid concentration in the tissue, by immunohistochemical and biochemical methods.
Result: after 24 weeks, hyaluronic acid concentration increased in both groups, but the effect was greater with estradiol.
The authors conclude that both treatments may enhance hyaluronic acid in postmenopausal skin, but oestrogen produces results greater than those from isoflavones.
How to read it.
First, there was no vehicle-only arm. An active went onto both sides. So from 'it rose after applying' you cannot subtract the act of applying and 24 weeks of time. It is the problem we set out repeatedly on the PRP page.
Second, the endpoint is concentration in tissue. Hyaluronic acid did rise, but this trial did not ask whether that showed on the face. This site has a separate page for hyaluronic acid; read it alongside.
Third, it is 15 against 15.
So it sits at 'not established'. The design is a double-blind randomised trial; the comparator and the endpoint narrow what it can answer.
- Randomised controlled trial in people · 30 participants · 24 weeks · Compared with another active ingredient · Funding not declared · Endpoint biopsy findings PMID 23435032
Collagen rose too — and again oestrogen was significantly superior
A 2017 trial. Same institution, same design, same size.
30 women aged 45 to 55 not on systemic hormone therapy took part, in a prospective, double-blind, randomised controlled design. Topical oestrogen or genistein for 24 weeks, with preauricular skin biopsies again used to compare facial collagen concentration before and after.
Result: type I and type III collagen both increased with both treatments. But the oestrogen group's outcomes were statistically significantly superior to the genistein group's.
(The p value is mistyped in the paper's abstract, so we do not carry the figure across. We record only that it reached significance.)
Two things to add here.
First, this report may be the same trial as the 2013 one above. Same group, same design, same 30 people, same 24 weeks, same biopsy site. The abstracts do not state the relationship. We have tied them so as not to count one trial twice. Writing evidence thinner than it is seems better to us than writing it thicker.
Second, the authors state an unknown themselves. We carry it across as written — whether prolonged use of topical genistein and other phytoestrogens could produce systemic effects is still unclear, and further research is needed.
That sentence should be the heaviest thing you read on this page. Resembling oestrogen is the reason this ingredient might do something, and equally the reason nobody knows what else it might do. If you have a history of breast cancer or a hormone-related condition, check in a consultation first.
- Randomised controlled trial in people · 30 participants · 24 weeks · Compared with another active ingredient · Funding not declared · Endpoint biopsy findings PMID 28508697
How to use it
- The trials used a 4% gel for 24 weeks. Concentrations in products on sale are usually not stated.
- They ran 24 weeks. That is not a basis for judging it sooner.
- What was measured is concentration in tissue. We did not find a trial measuring how much this ingredient changes what the mirror shows.
- For thicker evidence on wrinkles and firmness, retinol, retinaldehyde and sunscreen are far thicker on this site.
- How to handle skin changes after menopause is not settled by one ingredient. Decisions involving hormones belong in a consultation.
Cautions
- It resembles oestrogen. With a history of breast cancer, endometrial disease or a hormone-related condition, check in a consultation first, even for an applied form.
- Whether prolonged use has systemic effects has not been established. The authors of the 2017 trial say so themselves.
- The trials did not report adverse events separately. There were 15 people per arm.
- We could not find data on use in pregnancy or breastfeeding. Weigh that alongside its resemblance to a hormone.
- Swallowed soy isoflavones are not covered on this page. Applying and swallowing are different questions.
With a new ingredient, apply a small amount somewhere inconspicuous, such as the inner arm, for two days first. Stop if it reddens or stings.
Related skin concerns
What this article relies on
- PubMed — 미국 국립의학도서관 문헌 데이터베이스National Library of Medicine · Checked on 2026-09-16