Violins and other instruments are like children, needing protection from unkind elements. Extreme temperatures and humidity pose the biggest threats.
For every thing there is a season. Fine violins can perform in all four seasons (as Vivaldi well understood), as do cellos, violas, and string bass. The only thing to remember is that stringed instruments, like people, need to adjust from winter to spring, spring to summer, summer to fall, and fall to winter once again.
This is because these are instruments made of natural materials – different types of wood, horsehair, and some metals, although strings are only rarely made of sheep intestines (more typically aluminum and steel filaments) – they respond to temperature and varying humidity.
Complicating that to a great degree are the different types of wood used to build violins and other stringed instruments. These are maple, spruce, and ebony, each of which absorbs ambient humidity to different degrees. This means that at the joints where those woods meet there is uneven expansion and contraction. As a preventive measure, the glues used to join those parts are chosen to shatter in extreme circumstances such that the wood itself doesn’t crack or break. A visit to a qualified violin maker after that kind of breakage is necessary to restore it to playing condition.
The problems caused by changing temperatures and humidity can include when the bridge sits higher than what is optimal (strings sit higher off the fingerboard), cracks and open seams, and softened varnish (permanent impressions can be made in the finish). A bow, too, can be affected by humidity, affecting its tautness.
But there are ways to avoid damage from extreme heat, extreme cold, and sudden changes in humidity:
Keep it in the case – Your case is a bit of a buffer to temperature and humidity swings. This is reason enough to store it inside the case, not leave it out. When traveling, be conscious of placing it in the sun or near a heat source. When you arrive at a concert hall or any other location expect the conditions there will be different from your home. Open the case and allow time for the instrument to adjust to the different environment. To be clear, only a hard case provides this protection.
But a case is not impermeable armor. If you leave it in an enclosed vehicle, in summer or winter, the temperatures can still cause expensive damage.
Wrap it in silk – There really isn’t a scientific explanation for this, but a silk wrapping around a violin slows the transfer of humidity, in and out, according to seasoned players.
Use technology – Humidifiers and dehumidifiers made for use inside an instrument case (Dampit is a common brand), as well as in the room where you are playing, can temper the ill effects. If the cost of repairs doesn’t provide enough incentive to take these preventive methods, here’s something else that might motivate you: A violin in the repair shop is a violin that isn’t being played.