Sometimes the cloth gets so dirty you can see it. Or it even re-greases your lenses! All the dirt, dust and fat rubs off on the cloth. This is exactly what the cloth is made for. After a while it is so dirty it will not clean your glasses properly anymore. What to do about it?
Cleaning cloths are generally made of a micro-fiber which is easy to keep clean. There are many ways you can do this:
Simply shake out the dust and dirt.
Wash by hand
Use cold water. Add a few drops of mild soap that is bleach free and which does not contain fabric softener. Let the cloth soak in the soap for a few minutes and then rinse it clean in cold water.
Wash in a washing machine
Use bleach free detergent, and it should be free from fabric softener. Let the cloth air dry when finished.
Washing the cloth regularly allows that you can reuse it. If you have a high quality cloth it should not be a problem to wash it multiple times. Washing opens the gaps between fibers so it will catch dust and dirt from your glasses again. In addition, micro-fibers are positively charged and this is perfect for dust and dirt which is negatively charged. Wash the cloth and let physics do the job for you!