Trifolium pratense, commonly known as red clover, is a member of the Fabaceae or legume family.
Red clover extracts are composed of varying amounts of isoflavones, flavonoids, pterocarpans, coumarins, tyramine, daidzein, genistein, formononetin, biochanin A, coumestrol, and naringenin, and all of these, except formononetin, have been found to bind to estrogen receptors.
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Isoflavones are hormone-like chemicals that are changed in the body to phytoestrogens which are similar to estrogen. When used as a dietary supplement or as a medicine red clover extract has been associated with bleeding disorders and increasing the severity of hormone sensitive conditions (breast cancer, endometriosis, fibroids, etc).
It is widely documented that use of red clover extract has estrogenic effects in the human body. Dietary supplements of red clover are being assessed as an alternative to traditional hormone replacement therapy and treatment of menopause symptoms. Many studies found side effects including weight gain. There are significant gaps in the research, and therapeutic use is limited by the lack of clinical evidence.
Possible benefits of red clover flower extract include reducing the effects of skin aging induced by estrogen deprivation. Red clover isoflavones have been correlated to an increased number of blood vessels, collagen fibers, and elastic fibers in the treated skin of postmenopausal women. Isoflavones did provide effective photoprotection and are good candidate ingredients for protection against ultraviolet (UV) photodamage.
There are a host of concerns regarding the effects of phytoestrogens. Personal history, genetic markers, etc. may put you at higher risk for the endocrine disrupting effects of phytoestrogens. It’s important to note beneficial effects were found in postmenopausal women, not people with otherwise normal estrogen levels. More research is needed to determine if the benefits outweigh the risks of using red clover extract medicinally. Even WebMD says there is not enough evidence to rate the safety of topically applied red clover extract.
Relevant Scientific Reading: The pros and cons of phytoestrogens, In vivo estrogenic comparisons of Trifolium pratense (red clover) Humulus lupulus (hops), and the pure compounds isoxanthohumol and 8-prenylnaringenin and Effects of one-year treatment with isoflavone extract from red clover on prostate, liver function, sexual function, and quality of life in men with elevated PSA levels and negative prostate biopsy findings.
What’s all this have to do with your hair? We’re getting there…
We are commonly asked about the safety of ingredients known to have adverse side effects when consumed. At this time, evidence does not conclude that when compared to oral consumption, absorption of topically applied substances reach the bloodstream in the same amounts or have the same effects on the body.
The permeability of skin is of an order of magnitude less than that of the intestinal epithelial cell membrane. Only substances capable of passing thru the stratum corneum (hydrophobic layer) and the epidermis (hydrophilic layer) will reach the circulatory system. In other words the skin is a very effective barrier. Skin penetration through skin appendages (hair follicles) is being investigated as a pathway for particles to reach the circulatory system.
Researchers studied the transdermal absorption of phytoestrogens. Findings indicate there is moderate adsorption of genistein and diadzein. Results suggest that initial applications are excreted in the urine, but repeated applications are captured in the skin.
A 2016 study found formononetin extract positively influenced hair growth on hairless mice. There is not extensive research evaluating topical application of red clover as it relates to hair growth. Other studies evaluated oral use of red clover extract & its effect on hair growth.
To put simply, the research is not conclusive in regards to the overall safety of red clover extract.
What does all of this have to do with shampoo? Keep reading!
A 2015 patent for compositions enhancing hair growth wrote that it’s not clear which of the isoflavones was considered to be responsible for the beneficial effects on hair growth. Every plant and even every part of a plant has its unique isoflavone fingerprint that contributes to the activity profile of the botanical extract made from that part of the plant. Because of these unknowns the recommended amount to include is somewhere between 100ppb & 2ppm. Yes! That ranges from parts per BILLION to parts per MILLION. 😯 uncertain much?
If you take the time to read any of studies. It’ll be helpful to know what anagen (active growth phase of hair follicle) and telogen (resting phase of the hair follicle) mean.
Preliminary research indicates hair growth can be stimulated by phytoestrogens in red clover extract. More specifically, the combination of a biochanin a & the peptide acetyl tetrapeptide-3 (aka capixyl TM) has been used to treat male pattern baldness. Researchers are working to determine important factors influencing baldness and how these ingredients may help.
However, exact mechanisms are not known & there is not enough research to rate safety for human use. Extracts are not chemically standardized and differences in activity may be attributed to the different chemical composition and dosing concentrations. This specific combination of ingredients has not been thoroughly researched and is not approved by the FDA.
Relevant [non-scientific] Resources related to the current class action lawsuit covering another product with Capixyl/Red Clover:
So let’s start with some background information on Capixyl– the FDA routinely charges cosmetic companies with their own safety verification before market, meaning there is usually no ingredient review by the FDA or other entity. Capixyl is currently not approved by the FDA. The other product line containing this same compound has had class action lawsuits brought against it, which are currently ongoing. Reports in these lawsuits include hair loss, fertility issues, hair damage and breakage, scalp sores and all over body rashes.
Non Scientific information to consider about Capixyl: