We take to our cruises a humidifier and we have never had any problems.
My wife suffers from eczema and she has to use essential oils (lavender and chamomile). Plus the humidity level should be at least 45%. That's why we bought a humidifier which has a trail for essential oils - a great find for my wife. Before we've found it in one of the reviews, I have never known that it is possible to maintain the humidity and to diffuse oils simultaneously. The brand is Everlasting Comfort, if I'm not mistaken.