Allergies, are the easy part because as everyone said you can take something for that. The humidity/smell is the challenge here. The solution I would suggest is the same one uses in moist basements. Home Depot and such carry these desiccant bags that you can hang and will adsorb the smell and moisture. You might be able to hide them so as not to offend the host or your friend. Below is a link to a similar product just to give you and idea what to look for. Good luck

http://noodor.com/p/moisture-absorbi...emove-dry.html