Machine drying (or tumble drying) is easy and convenient but has drawbacks. Do not use the dryer on items unless the wash care label advises. Even then, proceed with caution. High, dry heat can change the appearance, quality, and fit of your precious items. 

The dryer will shrink fabrics using natural fibres like linen, cotton, viscose, silk, rayon, and wool if they aren’t pre-shrunk before garment manufacture. Synthetics like polyester, acetate, spandex, acrylic and nylon will retain their shape, even in excessive heat.

Pick a cycle without heat if tumble-drying is the only option. Press the garment afterwards if needed. Buy cotton underwear a size larger if you prefer to tumble dry with heat. Conversely, feel free to machine dry clothing that you deliberately want to shrink.