The reason of easy to be foggy for the contact lenses may be the reaching of expired time. You should check how long you have used it. If it is near the expired time, the water content character of it is losing. That is why you feel the contact lenses are easy to be foggy. I suggest you to change the new one.
I never heard that contact lenses will fog up in eyes. It mostly believed that eyeglasses lenses are easy to get foggy. If your contact lenses fog up in your eyes, you probably have heavy depositer. You'd better your eye checked and ask your eye doctor to prescribe you some contact lenses according to your vision needs. Besides, you also need to take care of your contact lenses and do not wear it when you sleep.
As we know, we just can use our contact lenses within a definite time. So when you use your contact lenses too long, maybe it is a bad way for you to use it anymore. Because our eyes can produce a kind of protein. Once your contact lenses stick this kind of protein, they will be polluted. At this time, it is better for you not to wear your contact lenses any more. That is why your contact lenses are easy to be foggy. At last, I advise you to buy a new pair of contact lenses and clean them regularly.