Sweet fern is one of those herbs that is fun to use. There's no need to apologize when you hand someone a cup of sweet fern tea or when you lead them to a sweet fern bath. Most people like the flavor and the scent. It's not like trying to coax them into drinking a cup of barberry root tea. And drying sweet fern will make your herb room smell wonderful.
What sweet fern is mainly used for is as a wash for itchy rashes like poison ivy or bug bites. It is easily made into a strong tea then allow it to cool, dip a cloth into the tea and wipe down the affected area. For larger rashes it is often just easier to pour that strong tea into a bath, giver the person an oatmeal filled cotton bag, and let them soak while rubbing the oatmeal over their skin. I also powder the dried leaves, mix them with dried plantain leaves and slippery elm bark. This I keep in my picnic baskets and coolers. If the bugs bite too badly water can be added to this powder to make a thick paste and smear on the bites to sooth them. I have had several of these spicy smelling, tiny poultices on my arms when the black flies are biting. Aaahhh, what a relief. It works well on bee stings as well.
Rubbing the fresh leaves on the skin acts as a bug repellent in the field and tucking a few leaves into your hat band may even keep the flies from flying around your head.
I do add a bit to any teas that are made to help with long term diarrhea. It does help to "dry up" loose stool that is persistent and helps other herbs go down a bit easier. I don't usually try to cure diarrhea for the first day or so because obviously the body is trying to get rid of something, but if it hangs on the person can get too dehydrated and needs to be treated. A few blackberry leaves or if entrenched blackberry root bark and some sweet fern leaves will usually gently end loose stool. Add a bit of cramp bark and vervain to settle down cramping muscles and the suffering person can finally rehydrate and rest.
If there are infected sores in the mouth I will again add sweet fern to the gargle to make it more pleasant and to help take down swelling.
Then there's just lining fresh leaves into my berry gathering buckets to keep the berries fresher longer. I also will put some into a simple syrup or honey to use as flavoring for wines and cocktails.