As to the uses for Common Plantain ( i'm assuming the weed that grows everywhere and not the banana) the action you are seeing is anti-inflammatory. I probably would help a bit with allergic reactions by reducing the swelling. However it will not be a substitute for epi-pens or benedril. If you are trying to take it internally with teas or just eating it raw, it is diuretic (makes you pee) expectorant ( makes you cough) and decongestant ( the reduction of swelling ie anti-inflammatory). the narrow leafed variety is used the same way.