People have been taking milk baths for hundreds and thousands of years. Cleopatra was known to take baths of milk, honey, and oils. Medieval women believed bathing in milk would help keep their skin white as milk. There are very legitimate benefits to bathing in milk, but most adult milk baths call for whole milk, or even dried/powdered milk.
I have a freezer full of breastmilk. My child still more or less refuses to take a bottle. Other than saving some bags to mix with cereal, I just don’t need all of that milk. When she was a few weeks old she started getting a bit of cradle cap and I had read that bathing her in a bath with some breast milk would help. Milk, especially breastmilk does have a number of benefits. Most of these benefits help with skin issues: dry skin, eczema, cradle cap, and softening the skin. It can also help relax and get ready for bed!
I filled her little tub with fairly hot water…stay with me here, I don’t try cooking my child. I had 4 bags of milk for a total of about 20oz of milk. 
I put the 4 bags in the hot water to start melting them, once the frozen milk had melted enough, I dumped the bags. I more or less had 4, 6oz milk cubes floating in the water HENCE, using extra hot water initially, I knew it would cool from the frozen milk. By the time the milk melted, it ended up being the perfect temperature.
I let her play, splish splash, and hang out for about 15 minutes before washing her hair and rinsing her off. The great thing about this bath is you do not have to use additional “clean” water for rinsing. It is actually better to just bath in the milky water to reap the benefits of the rich, fatty, goodness! After wriggling her out, I pat her dry as to not wipe off the milky goodness! I then apply a blend of lavender, melaleuca, and frankincense oils in whipped coconut oil to her legs and arms to help with dry skin and lock in the creamy balm. I continue with our regular bedtime routine of oils and such.
Additions: Sometimes I will add a drop of lavender to about 1tbsp of epsom salt to add to the dream inducing capacity of the milky bath.
The Nurtured Bee 