Hand wash with mild detergent. Line dry in the shade.
You may notice some wear or fading of the cotton fabric trim after extended use. This is normal for any natural fiber, like cotton, when exposed to regular sunlight and friction; it will not affect the durability of the nylon webbing base.
Only you can accurately assess the safety of your pet's collar. If you ever notice any type of damage, do not use the collar with a leash as your pet's sole restraint.