Mix the mashed root with water and use for skin inflammations.
"Whosoever shall take a spoonful of the Mallows, shall that day be free of all diseases that may come to him." - Pliny
Euell Gibbons (in Stalking The Healthful Herbs) recommends mixing water used for boiling marshmallow roots with equal parts honey and orange juice, and using a tablespoon full at a time for coughs and minor throat irritations.
Marshmallow grows really well in zones 6 & 7 in full sun & relatively dry/crappy soil (ie on retaining walls). It's a pretty plant-- 4-5' with small (1")white/rose throated hollyhock type flowers & soft fuzzy leaves that make great faerie houses. Prolific reseeder. Harvest the root in the plant's third year, clean & simmer 20-30 minutes until water is gooey, or cut & dry for later use.