Epsom salt (or Epsom salts, as it is sometimes known) has little in common with its culinary and cosmetic salt counterparts, sea salt, table salt and kosher salt.
Epsom salt is hydrated magnesium sulfate, a chemical identity that the other salts do not share. Table salt, kosher salt and sea salt are all at least 97.5 percent sodium chloride, though sea salt also contains minerals like iodine, magnesium and potassium.
Though table salt is typically fine, and kosher salt is typically large and course, Epsom salt and sea salt can be found in various consistencies. Epsom salt is colorless and clear, however, while sea salt has a cloudy appearance.
Sea salt is used in cosmetics and food preparation; kosher and table salts are used primarily with food. Epsom salt, however, has comparatively less culinary value due to its inferior, bitter taste. In fact, Epsom salts are often called "bitter salts." Epsom salt is used as a cathartic in medicine, a magnesium-boosting fertilizer in soil and an aid in fabric dyeing and leather tanning.
Some people put Epsom salt in their bath water to help draw out impurities through their skin's pores and to relieve skin problems, muscle soreness and injury. Epsom salts are commonly used for this purpose, but there is no medical evidence of these baths' effectiveness. The other salts are not typically used for this purpose.
Epsom salt gets its name from the mineral-rich waters in Epsom, England where it was originally extracted.