Epsom salt is not salt. It is magnesium sulphate, named after the English town where it was first drawn from the springs, and what it does for feet has nothing to do with sodium.
Dissolved in warm water it does three things at once: it draws fluid out of swollen tissue, it softens hardened skin, and it eases aching in tired muscles and stiff joints. That range is why it appears more often than almost anything else in natural foot care.
The standard soak
Half a cup of Epsom salt to a basin of comfortably warm water. Fifteen to twenty minutes. That is the whole recipe, and it covers aching, swelling, stiffness, and softening skin before you work on a callus.
Two details people get wrong. First, the water should be comfortably warm, not hot — hot water dries skin and offers no extra benefit. Second, twenty minutes is a limit rather than a target. Skin left soaking longer becomes waterlogged and fragile.
How often
For an ongoing problem such as arthritis or feet that ache from standing, three or four times a week is reasonable. For a specific episode — a sprain, a flare of gout, a callus you are working down — nightly for a week, then taper.
Daily soaking indefinitely is not better. It strips the skin's oils, and dry cracked skin creates its own problems. Always moisturise afterwards.
Before filing a callus
Soak first, every time. Twenty minutes turns a callus from rock to putty, and softened hard skin can be filed gently with a pumice stone instead of attacked.
Never cut hard skin with a blade. It is very easy to take too much, and the wound that follows is worse than the callus was. More on calluses.
Making it work harder
- Aching or tired feet: add six drops of eucalyptus or peppermint oil.
- Cold feet: add grated fresh ginger, which genuinely widens surface blood vessels.
- Odour or fungal concerns: add ten drops of tea tree oil.
- As a scrub: two tablespoons of Epsom salt into a tablespoon of olive oil, massaged over damp feet.
Who should not soak
This is the part usually left out. If you have diabetes, do not soak your feet without asking your doctor first. Nerve damage can hide water that is too hot, and softened skin is easier to break and slower to heal — the exact conditions that lead to ulceration.
Nobody should soak broken skin, an open blister or an ulcer. Test the water with your elbow or a thermometer, never your foot.
The full entry, including quantities for scrubs, is on Epsom salt.
Does the magnesium absorb?
This is the claim you will see everywhere, and it is worth being straight about. The idea that magnesium passes through the skin in useful quantities during a soak is not well supported by evidence. The studies that exist are small and inconclusive.
That does not make the soak useless — it makes the reason different. What Epsom salt reliably does is osmotic: it draws fluid out of swollen tissue, and it softens the keratin in thickened skin. Add warm water, twenty minutes off your feet, and the relief people report is real even if the mechanism is not the one on the packet.
So buy the cheap bag rather than the boutique one. There is no meaningful difference between plain agricultural-grade magnesium sulphate and a scented tub at five times the price, beyond the scent. If you want the aromatherapy, add your own essential oil to the cheap bag and keep the change.