Hi Alison,
Make sure you use it before you go.
A friend of mine bought a travel hairdryer on her hols and was asked at check in if she had any electricals to which she replied yes, they then asked if it had been used and she said no. They told her to take it out of the suitcase/hand luggage and had it confiscated.
I don't know why they did this, maybe they were short on one for themselves and needed a new one!!
I don't know if it applies to all airlines but this was Ryanair.
I would suggest you use it a couple of times just to be sure.
Gail xx