When I'm sore from workouts, or being sick, or whatever, I take a bath with epsom salts. It's lovely and it almost always works to get the pain away.
I looked up shampoo use:
"The salts do wonders for the hair, absorbing oil from problem hair by adding 8 tablespoons of Epsom salts to a half a cup of shampoo thats formulated for oily hair. Put a tablespoon of the shampoo mixture on dry hair and work it in and around the scalp area, rinsing it out with cold water. To rinse it well, and further treat oily hair, pour a cup of apple cider vinegar over the hair, leave on for 5 minutes, and then rinse with cool water. To add fullness to thin hair, combine equal parts of Epsom salts and hair conditioner. Warm the mixture in a pan then work it into hair. Leave on for 20 minutes and rinse with warm water. "