Ask Dr. Pete: What are Optical Brighteners and Why Should We Care?

Before we dive deep into the exciting world of optical brighteners (we know you’re on the edge of your seat), we want to tell you a bit about Dr. Pete.

A product inventor, innovator, and sustainability expert, he’s the brains behind our Bio Laundry Detergent and was a founding member of The Sustainability Consortium. Previously in our The Dirt series he’s covered topics on such things like, Hard Water and How it Affects Our Cleaning, What is Green Chemistry, and How to Remove Balsamic Vinegar Stains. Now he’s back to explain what optical brighteners are and why you should care.

Ok, so what are these things we keep hearing called ‘optical brighteners?’

Optical brighteners are often referred to as fluorescent whitening agents. Essentially, they are large molecules composed of (excuse my Science) phenyl and heterocyclic groups with conjugated double bonds. Most optical brighteners used in consumer products such as laundry detergents are with stilbene derivatives (1) or biphenyl derivatives (2). Fun fact: Stilbene means “glittering” in Greek.

What is Stilbene used for?

Before these fluorescent molecules were invented in the 1940s, blue dyes were used in laundry detergents and textiles to add a little bit of blue hue to help offset the “yellowing” of white clothes and linens due to aging and staining. But those blue dyes only make laundry visually appear whiter, not brighter. The fluorescent optical brighteners work differently by absorbing invisible UV light and turn it into visible lights in blue color. Once deposited on laundry fibers, those fluorescent molecules make clothes and sheets appear to be both whiter and brighter by hiding the yellowing hue away from our visual detections. Optical brighteners have gained huge popularity in applications for laundry detergents, textiles, cosmetics, paper, and hair care products over the years. Nowadays, millions of pounds of optical brighteners are used and discharged as wastewater into our ecosystems every year. 

Are they harmful for clothes, people, or the planet?

There are more than 400 optical brighteners that have been made in history. Due to performance, health and environmental concerns, less than 50 of them are still in mass production for commercial uses. Those remaining have much more acceptable safety profiles in terms of their toxicity to the environment and human health. However, they remain as concerned chemicals in commercial applications such as laundry detergents for the following reasons:

1. Lack of biodegradability

Once discharged as wastewater, those optical brighteners escape from water treatment plants and get released into open or underground water. They biodegrade slowly and may end up accumulating in marine lives. Some optical brighteners are acutely harmful for aquatic organisms.

2. Reproductive toxicity concerns

Under natural lighting, those optical brightener molecules slowly go through a photodegradation (the alteration of materials by light) process and break down to smaller pieces as metabolites. The data from a few research reports suggests that potential estrogen disruption and reproductive toxicity concerns from certain stilbene derivatives and their metabolites need to be further investigated.

3. Potential irritation to sensitive skin

The functionality of optical brighteners has NOTHING to do with laundry cleaning.

They are designed to dissolve in water and then absorb onto laundry fibers during the washing cycle. Resisting to be rinsed off, they stay on fibers in order to create an optical illusion to make clothes and linens appear whiter and brighter. Once absorbed and accumulated onto laundry fibers after rinsing and drying, those optical brighteners and related metabolites are in direct contact with our skin and may cause harm for some people with sensitive skin.

Wow as nerdy as this all is, it’s pretty enlightening. So then, what is the future of optical brightening in laundry products or even within household cleaning products?

It’s really tough to say. What we do know is that our cleaning future (particularly for Dirty Labs) does not need fluorescent optical brighteners – it is not worth the risks and costs to just fool our eyes. We will need to get more accustomed to the fact that the fabric materials made of our white clothes and linens may carry a yellowish hue by themselves or become so over time. We do not need to make our clothes look so bright. Washing our laundry with less harsh, bio laundry detergents, and under cold water, while lowering our drying temperature and time, or just line drying will help retain the color and brightness of our clothes and extend their longevity. If white and bright shirts and bed sheets are strongly desired, using a bio laundry detergent in combination with an oxygen booster will most likely deliver the results without optical brightening.