You can tell by the type of fabric it is. If the fabric is very delicate it can not be washed regularly; while if it is not, most likely it can be washed like normal.

Yes, I guess so...I use it in my sewing of clothes and they get washed regularly!

No the age of the underwear does not mater as long as it is washed and changed regularly.

They are either never worn, washed regularly or may be treated with bactericides.

Launder your ferrets bedding means that it is usually a soft cloth material that needs to be washed regularly to keep odors down.