Saturday, December 17, 2011

What's Cookin' This Week: In the Bathtub

Magnesium sulfate heptahydrate - Epsom Salts!

Epsom Salt Soak (not really a recipe, just passing along the relaxation)

The recipe:
½ cup to 1 cup Epsom salts (depending on the size of your tub and depth of your bathwater)
©Science-y Hair Blog 2013
That’s it. Sprinkle the salt into the bathtub as it fills and mix. Soak for at least 15 minutes – so bring a magazine, the newspaper, some music, or a good friend (a really, really good friend) and enjoy!
Be sure to rinse with fresh water or you’ll have a very tacky residue on your skin.
I prefer to keep my hair out of the water, or only give it a quick dunk and then wash out the salt.
Get your Epsom salts at a drugstore (pharmacy, druggist, chemist), avoid using the kind you buy at a garden shop.

The Nitty-Gritty©Science-y Hair Blog 2013
Prolonged exposure to very warm water is drying to the skin because the components of the top layers of the skin which retain moisture are water soluble.

But there are those days when sore muscles and joints or the need to relax profoundly, overwhelm concerns about skin. If you have never had a bath with Epsom salts, you don’t know what you’re missing.

Why/How Do Epsom Salts Work?©Science-y Hair Blog 2013
Epsom salts are magnesium sulfate (MgSO4). Just magnesium and sulfur and oxygen. And they’re not merely acting on your skin. While you might think of salts as being bad for skin, think of this: if you are swimming in fresh water and you get some in your nose, it burns, you sneeze. No fun. If you swim in the ocean and get salt water in your nose, no such reaction. When you have a skinned knee or a bad burn, it is far less painful to wash the raw skin with (sterile) saline solution than with plain water. Sterile saline solution is a good thing to have in your medicine cabinet! I buy sterile saline meant for contact lenses (this is not a contact lens cleaner) to wash nasty injuries. It’s especially good for kids and pets who don’t like to have wounds cleaned. My point is, Epsom salt isn’t likely to cure anything, but it won’t hurt you. I suppose one could hypothesize that the sulfate component (or just the "saltiness in general) could be good for treating oozing-type rashes like poison ivy or eczema, and it might discourage skin fungal infections, but I can’t back that up with any facts.

Deeper Than Skin Deep©Science-y Hair Blog 2013
The amount to use is about 1% Epsom salt. At this concentration, your body will actually absorb some of the magnesium and sulfur from the water. 1% was the reliable level required in a study conducted to test whether the minerals from Epsom salt could be absorbed trans-dermally, to increase blood levels of these minerals. Too much Epsom salt will make the water feel slippery or slimy. My bathtub is 54x23 inches, if I fill it with 5 inches of water (length x width x depth) that equals 6210 cubic inches (about 27 gallons or 102 liters). That’s not totally accurate, the back of my tub slopes. So I would add from  ½ to 1 cup of Epsom salts. Some of the subjects tested absorbed minerals at lower concentrations – so there is a range in the recipe. If you have a large tub and take a very deep bath, use 1 1/2 to 2 cups of Epsom salts.©Science-y Hair Blog 2013

After one bath, the test subjects had an increase in blood levels of magnesium of around 45% and a 50% increase in sulfate. After 24 hours, the magnesium has left your body, but the sulfate may be stored until your body has as much as it needs.

What is magnesium good for? Magnesium plays an important role in contraction and particularly relaxation of muscles. Maybe this is why an Epsom salt bath is so deliciously relaxing. You also use magnesium in the enzymes which control so many chemical reactions in your body, and in the process of manufacturing proteins to maintain and repair your body. And, of course, you need it in your bones! If you drink hard water, you get more magnesium than soft water drinkers. Otherwise, we get magnesium from fruits and vegetables, nuts, and whole grains.©Science-y Hair Blog 2013

Sulfate – now this gets really interesting. Sulfate is required to produce compounds in cartilage (chonrdoitin sulfate), lipids used in your brain (remember, your brain is mostly fat!). When your hair is actively growing, it uses chondroitin sulfate, and skin also uses chonrdoitin sulfate to stay healthy (chonrdoitin sulfate is part of connective tissue, which includes skin). The sulfate we ingest comes from protein-containing foods and from our drinking water. There is no RDA set for sulfur or sulfate, but if you don’t eat many protein-containing foods (you’re a vegan or nearly so), or have difficulty absorbing nutrients, a little extra sulfate might help and is not likely to hurt. As hair and skin go, too little sulfur in your diet can lead to easily-damaged hair and skin disorders.©Science-y Hair Blog 2013

You would have to take Epsom salt baths a number of times to increase the levels of these minerals consistently,  (okay, I need to correct myself here, sulfate is a salt by itself, not a mineral) but even if you rarely indulge in baths, I’ve just laid out another good excuse to slide into a warm tub.
©Science-y Hair Blog 2013
If you have a chronic disease such as high blood pressure, you should check with a doctor before using Epsom salts in your bath – altering the magnesium in your blood might be incompatible with blood pressure medication. And don’t drink the water from the bath or let your dog or cat drink the water, Epsom salts are also used as a laxative. The increases in magnesium and sulfate in blood from Epsom salts in bath water were determined to be safe for healthy adults only.

That's all for now - enjoy the soak.

National Research Council. "7 Sulfate." 2005 Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press.

Westgate GE, Messenger AG, Watson LP, Gibson WT. 1991 Feb;96(2):191-5. Distribution of proteoglycans during the hair growth cycle in human skin. Journal of Investigative Dermatology

Report on Absorption of Magnesium Sulfate (Epsom salts) Across the Skin
RH Waring, School of Biosciences, University of Birmingham. U.K.

Verges J, Montell E, Herrero M, Perna C, Cuevas J, Perez M, Moller I., 2004. Clinical and Histopathological Improvement of Psoriasis in Patients with Osteoarthritis Treated with Chondroitin Sulfate: Report of 3 cases. Medicina ClĂ­nica.


  1. Great article! I used to have loads of baths in salts, then switched to lovely bubble baths when I started making my own money, then stop soaking in the bath mainly when I worried that it might be making my coochie irritated (sorry, tmi!), buta lso partly because I used to almost blackout when I got out and now I take very rare baths with bubble baths again (plus a glass of water to drink). I never thought to go back to using Epsom salts.

    I have two questions:
    - if I soaked for longer (think MUCH longer *cough* hours *cough*), would the salts start to have a negative effect? I suppose I could just add them nearer the end though?
    - if I did dunk my hair, would I then wash it or should I wash it before? Does shampoo remove the positive effects on hair?

    Thanks for reading my essay!

  2. If you soak a very long time in the bath, your skin starts to look wrinkled on your fingers. A long time in the water dissolves the lovely humectants and washes away the lipids that keep your skin hydrated, so a long bath dehydrates your skin and the salt may make that worse, so it'a balancing act, for sure.
    If you get your hair in the salty water, be sure to rinse out the salt afterwards. The salts leave a very tacky-feeling residue on your skin and hair and it's rather unpleasant.
    If you keep the water on the hot side, your body goes into "cooling" mode, opening up the blood vessels nearest your skin and lowering your blood pressure. So I can see why you might feel like passing out when you made the temperature change from tub to air. Getting up slowly and sitting on the edge of the tub for a while first is probably a good idea.