Naturally, I’m always interested to read what the skincare bloggers and formulators have to say about this packaging’s potential.

But through the years I haven’t seen many articles out there that:

1. Go into the science/mechanism through which this glass works for preservation
2. Talk about the limits of ultraviolet glass. Specifically, can formulators use fewer preservatives if they are packaging in Miron. How much less?

So to help me demystify the science behind the glass, my friends at Infinity Jarsprovided me with the research behind their claims of how their UV glass bottles keep natural products and ingredients fresher, longer. They also sent me a nice assortment of their glass cosmetic bottles and screw top jars to use myself–thanks Infinity Jars! Here’s what I learned:

Ultraviolet glass bottles and UV rays

When we expose something to light, it reacts — it allows living plants to grow, it causes dead plants to wither. Light fades our wood decks and wrinkles our skin over time. It’s just as degrading as it is life-giving.

Clear glass (and some other types of glass) allows light in the visible spectrum to penetrate through, causing products to degrade more quickly and encouraging microbial growth.

Here’s where violet glass is different: it filters out light in the visible spectrum, letting in only UV light (UVA and UVB) and infrared.

The absence of visible light helps the product resist degradation, increasing a product’s shelf life.

But that’s just the first piece. While violet glass filters out visible light, it selectively lets in UVA and UVB rays, which actually suppress microbial growth. Many formulators use violet glass (also referred to as Miron glass) because it allows them to use fewer preservatives and antimicrobial ingredients in some types of products, while still maintaining freshness.

So let’s get a few things straight.

Violet glass vs. Amber

As previously mentioned, when you put a product into clear glass, you’re exposing it to light. As we know, light makes plants grow and speeds up the decay process in plants that have reached maturity. So, plant-based products packaged in clear glass are going to experience these visible light effects. Colored glasses, on the other hand (such as amber or cobalt blue), are particular in which types of light they let in.

There’s a big distinction here: amber glass blocks UVB and UVA rays and lets in light in the visible spectrum, whereas violet glass blocks visible light and lets in bacteria-killing UVA and UVB. Both types of glass let in infrared rays.

Ever noticed that beer and kombucha are often packaged in amber glass? Whereas violet glass selectively lets in UVA and UVB rays, amber glass blocks them. Because microbial activity makes beer and kombucha what they are, you actually don’t want to suppress microbial growth. So choosing amber glass for these products helps to block out UV rays and maintain desired fermentation.

For a clear illustration of how these different glasses allow and filter different forms of light, check out the illustrations on page 4 of this document.

The Power of UV

Knowing that the main mechanism of violet glass, championed by the company Miron, is that it selectively lets in light in the UV spectrum, I wanted to look at a few studies that show the effects of UV light on microbial activity.

I spoke with the company Infinity Jars, who pointed me towards some research in UV light being used to combat bacteria in dental applications. According to the Technical University of Denmark, there are multiple bacteria that come together in what is called a biofilm and infect an inflamed tooth root. (Just in case you weren’t already dreading your next visit to Dr. Smiley.) These bacteria have proven difficult to treat through antibiotics, and thus the dental industry is keen on finding and using alternative treatments.

Researchers at the aforementioned DTU experimented with different light wavelengths to eradicate these persistent bacteria and found that UVB was the most effective.

Similarly, the storage of injectable medical fluids (like blood) is a place where UV light can be helpful in staving off microbial growth. When chemicals are added for preservation, they may affect the way the patient receives them. An article in the Journal of Transfusion in 2016 looked at the effect of UV light on bacteria growth in blood plasma and found that UV light at 405 nm was effective in maintaining sterility. This could have huge implications for the way blood is stored and used medically.

And for us, it gives weight to the claims that storing your homemade, organic skincare products in a violet glass bottle could preserve its integrity without the use of excess preservatives.

But truthfully, I’m pro preservative

As a formulator and educator, I advocate for using natural, broad spectrum preservation systems to preserve aqueous products. If you’re making something with water, you must use ingredients that naturally suppress the growth of microbes. Because, although light contributes to the growth of unwanted bacteria or mold, it’s not the only factor, and there are so many variables with product formulation, it’s better to be safe than sorry.

Further, the studies I mentioned applied UV light directly to target bacteria, rather than violet glass. There isn’t a lot of research (or any, as far as I’ve found) that tells us how strong the antibacterial effect of violet glass is, and whether we can omit preservatives altogether, or use a different type or lower concentration. 

As organic skincare formulators, we want to get to the point where we can quantify with certainty how much preservative we should add to our products, depending on ingredients, manufacturing practices, packaging, and other factors. Put differently, the goal for some may be to test the limits of how little preservative they can use without sacrificing the safety and stability of their product. This can only be determined through proper testing.

Ultraviolet glass bottles are a great option

What I will say is that if you’re making an aqueous organic product and want to give it shelf life, Miron or Infinity glass is the best thing you can store it in. The benefits of the glass can only benefit your product.

If you make anhydrous products–products that do not contain water such as facial oils, balms, butters, salves, scrubs, etc–or sell dry herb or tea blends, then we can confidently say that ultraviolet glass bottles will give your ingredients and products the best shelf life. If your customers reuse their glass and resonate with top quality, then glass bottles from Infinity Jars might be a great option for you.

However, if you sell your product and your customer is price conscious, ultraviolet glass bottles might not be a feasible option for you.