"Optical brighteners" is a term used to describe certain chemicals or compounds that are added to products, such as laundry detergents or papers, to make them appear brighter or whiter. Full definition
It's not always possible to avoid brighteners since so many products do contain optical brighteners. (greenmountaindiapers.com)
I'm not sure if everyone is aware that this detergent still has optical brighteners in it that will build up in your clothes and diapers. (thirstiesbaby.com)
Detergents with optical brighteners do leave chemicals on your cloth diapers. (pinstripesandpolkadots.com)