Swanson's do Magnesium Oil
You can make your own
magnesium chloride bath or foot soak, instructions here.
Or here
Mark Sircus is a leading advocate of transdermal magnesium.
Epsom salts also works and MAY be better for people with arthritic conditions. (many spa waters are rich in magnesium sulphate it's possible the sulphate is helping as much as the extra magnesium)
There is a long history to
Hydrotherapy It would be surprising if their wasn't an element of truth to some of the claims.
It's quite easy to test out for yourself. A 25kg sack of magnesium chloride costs about £7 from agricultural or Equine suppliers. (It's for put in the drinking water troughs for animals suffering stress,) If you are under stress yourself or suffering muscle cramps in bed or find it difficult to get to sleep have a 20minute soak in a hot bath with a generous amount of magnesium chloride or sulpate in the bath water.
Flotation Therapy 2 min video
Bathing in a magnesium-rich Dead Sea salt solution improves skin barrier function, enhances skin hydration, and reduces inflammation in atopic dry skin.
I would like to see any evidence to support the claim that magnesium is not absorbed through the skin. It's certainly the case that the stuff they put in sunscreen appears in you urine within a couple of hours if those chemicals pass through skin I'l like to see the science proving magnesium does not.
If your skin is already dry and you live in a dry climate it's possible a very concentrated super saturated solution could dry on the surface of the skin and as magnesium is hygroscopic it could be drawing water out of the skin rather than the other way round. Swanson's have a warning saying
If skin irritation occurs discontinue use. the bath/footbath soak method is using a much weaker concentration and would hydrate your skin BEFORE going outside in the sun.
I also use an oral magnesium supplement AND make my own
magnesium mineral water
You know when you've absorbed too much magnesium, It passes into the colon absorbs water and lets you know it's time to reduce intake a bit.