An Epsom salt bath has long been a favorite remedy for everyone from grandparents to Jessica Biel—the latter of whom says she soaked in 20 lbs of them ahead of last year’s Met Gala.

But what exactly are Epsom salts and what makes them so special? And, do they really work for detoxifying and de-stressing the body and mind?

An age-old remedy

Just outside of London near the verdant Surrey Hills National Landscape, lies a medieval hamlet built around mineral springs. This town is called Epsom, and until the late 17th century, it was a renowned health resort. This is where Epsom salts—a naturally occurring magnesium and sulfate mineral compound—were originally discovered.

According to tradition, soaking in a hot bath infused with these therapeutic salts allows the magnesium and sulfur to penetrate the skin, soothing muscles, detoxing the body, and easing stress.

The benefits of soaking in Epsom salts

The benefits most commonly associated with using Epsom salts in a hot bath have to do with reducing inflammation and easing muscle pain. Skin-wise, the concentration of magnesium and sulfur in warm water is said to help open pores, eliminate dead surface cells, and improve skin hydration levels. Some also say that soaking in salt baths can help restore the body’s electrolyte balance and promote the proper functioning of the cardiovascular system, muscles, and nerve tissue. Many also claim that the minerals help reduce blood pressure and calm the nervous system, thus soothing stress and improving sleep quality.

On social media, you’ve also probably seen claims that Epsom salts can be used to create a “detox bath” thanks to sulfur’s supposed ability to eliminate toxins from the body and drain excess fluids from the body.

Sounds great, right? However, as is often the case with ancient remedies, there isn’t a ton of scientific evidence that supports the claims around Epsom salts, and the studies that do exist are limited. Some skeptics say that magnesium could never penetrate the skin deeply enough to reach the muscle; others speculate that many of the purported benefits of Epsom salts might just be due to the heat of the water used in the bath.

Regardless, that doesn’t stop many doctors, fitness professionals, and physical therapists from recommending Epsom salts in the treatment of muscle pain and fatigue. And, anyone who has ever taken an Epsom salt bath or soaked their feet in a tub of Epsom salt-infused water can probably attest to the blissful experience. As it stands, age-old remedies are age-old remedies for a reason—they probably wouldn’t continue to be popular if many people didn’t experience some benefits over the years, real or imagined.