Have you checked your house recently? Have you seen any nasty stains or marks? If you have cleanliness problems on your floors and tiles then you might have mildew problem. 

Mildew means fungus or mold. These are very kinky and dangerous stuffs. All types of fungus have the ability to spread illness and it is their basic characteristic to spread disease.  They reproduce by generating spores and the spores are released into air. These spores land anywhere and they can reproduce in any organic planes like tissue papers; wood plane and food like bread are mostly affected, cloth, carpet and so on. They are mostly attracted by darks corners and warm places like under the carpet, they also like humid places so they are mostly found in wet places like bathroom. They can cause diseases like asthma, skin diseases and many other cardio vascular diseases. Some of these diseases can be deadly and life threatening that is why mildews are something to be afraid of. 

There can be lot reason of mildew attack. First of all if your house has too much moisture then it is sure that it will caught mildew problems as they are mostly attracted by moisture. Too much raining or leak in your plumbing system might cause that problem. If you have leak problems then fix it as soon as possible. The more time they last the griever your position would be. So do not wait call a plumber and fix that leak. If the moisture is caused by rain or other natural problems then there are special sprays available in the market that can remove moisture.  

Your house might have fungus infections from an alien object that has carried the fungus spores from some other house with fungus infection. In that case you will have to follow the normal rule. If the fungal infection has spread in a lot of place then you will have call the fungus controlling firm and ask them to take care of this mess. You will also have to quarantine some stuff that has fungal infections or they will spread mildew in the future. If the object is not that important and is inexpensive then the best thing to do with it is to burn it.  

Once all the fungus has been removed you can move into the house and from that time you will have to take special care. Do not let any fungal infections grow, use bleach but be careful when using bleach. Bleach might cause permanent discoloration to colored object. You will have to look for fungal infections and when you find it do not wait destroy it.