SAN FRANCISCO—San Francisco-based obstetrician gynecologist (OBGYN) Jennifer Gunter published a personal letter to actress Gwyneth Paltrow expressing her opposition to jade vagina eggs, a product sold by Paltrow’s online lifestyle firm, Goop.

When asked about the product in a Q&A session with Goop, customer Shiva Rose said:

“Jade eggs can help cultivate sexual energy, increase orgasm, balance the cycle, stimulate key reflexology around vaginal walls, tighten and tone, prevent uterine prolapse, increase control of the whole perineum and bladder, develop and clear chi pathways in the body, intensify feminine energy, and invigorate our life force. To name a few!

The jade creates kidney strength—it’s known as jing in Chinese energy, and it’s all about sexual potency, and even beauty—if your hormones are balanced, your skin will look better. It’s a holistic combination of things, where one benefit builds to another. Jade also takes away negativity and cleanses—it’s a very heavy material, very powerful.”

Dr. Gunter—who specializes in pelvic floor disorders and infectious disease—blogged that since its release, several people have inquired about the jade egg, and she felt it was necessary to reach out to Paltrow publicly.

The letter opens by condemning the effects of jade eggs as a “load of garbage,” and continues on to critique a number of claims about the product – like that it balances hormones; she argues that it is “biologically impossible” for the jade egg to contain hormone-balancing properties and that long-term use can be detrimental to a woman’s health. Gunter criticizes several of the product’s recommendations for usage, like insertion before sleeping and/or walking around, stating that the jade egg is permeable and could potentially increase the risk of bacterial vaginosis (BV) or toxic shock syndrome (TSS).

In a follow up blog post, Gunter called attention to Goop’s reply, which consisted of a product disclaimer stating:

“The views expressed in this article intend to highlight alternative studies and induce conversation. They are the views of the author and do not necessarily represent the views of Goop, and are for informational purposes only, even if and to the extent that this article features the advice of physicians and medical practitioners. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment, and should never be relied upon for specific medical advice.”

“I’m always concerned about the erosion of science,” Gunter told Gizmodo in an interview. “People keep telling me that this is eastern medicine practiced for centuries, so how could it be bad?…There are a lot of ‘ancient’ practices we now know are bad. I’d rather my science be biologically plausible.”