Rapid changes in temperature can cause condensation inside the watch. If you notice moisture beneath the glass, you should immediately go to a watchmaker, who can open and dry the watch. Even if the signs of moisture disappear, by themselves… the moisture will not – and will eventually damage your watch – so, visit a professional and remove it permanently. Even waterproof watches are not protected against condensation, so keep that in mind if you plan to go from very hot to very cold temperatures – like from a hot sauna directly to the snow. If condensation occurs, it very rarely (if ever) depends on manufacturing, so if your watch is damaged by moisture, the warranty will probably not cover it (it could be manufacturing issues, but… most likely it will be because of the rapid change of temperature = natural causes).