Bisphenol A (BPA) is a chemical compound widely used in manufacturing, primarily to produce certain plastics and resins. Its presence in consumer products, including the lenses and frames of some sunglasses, often raises public concern about safety. Evaluating the actual risk requires understanding how BPA functions in the material and the mechanisms of exposure through eyewear. This article explores BPA’s role in sunglasses, potential exposure routes, biological concerns, and safer alternatives.
Understanding BPA’s Role in Eyewear
BPA serves as a precursor molecule in the synthesis of polycarbonate plastic, a material frequently chosen for sunglass lenses and sometimes for frames. Polycarbonate is highly valued in the eyewear industry for its exceptional impact resistance, durability, and lightweight feel. BPA is also sometimes found in epoxy resins used as coatings or adhesives in specific eyewear models.
The final polycarbonate material is a polymer, where BPA molecules are chemically linked together in a chain structure. Since the polymerization process is not always complete, trace amounts of residual, unreacted BPA monomers remain trapped within the solid plastic. These minute residual amounts raise concerns about potential exposure to the wearer. The material’s desirable properties, such as its shatter-proof nature, are directly linked to the use of BPA in its creation.
How BPA Exposure Occurs Through Sunglasses
Exposure to BPA from sunglasses occurs primarily through the migration of residual, unreacted chemical from the solid plastic to the skin or mucous membranes. This migration, or leaching, is influenced by how sunglasses are used and stored. Since polycarbonate is a solid material, exposure is considered dermal or mucosal, unlike the dietary route common for food-contact plastics.
Heat is a significant accelerator of chemical migration from plastic materials, and sunglasses often face high temperatures. Leaving glasses in a hot car or wearing them in direct, intense sunlight increases the rate at which residual BPA diffuses to the plastic surface. The chemical can then be transferred through direct skin contact, particularly where the frames meet the nose pads and temples. Dermal absorption is further enhanced by sweat and natural skin oils, which act as a solvent to draw the chemical out of the material.
While less common, oral exposure can occur if a person habitually chews on the plastic frame arms. However, the estimated upper-end dermal exposure from wearing polycarbonate eyewear is considered low. Testing simulated exposure by incubating components in artificial perspiration found that the amount of BPA transferring to the skin was well below established safe limits.
Evaluating the Health Concerns of Eyewear BPA
The primary health concern regarding BPA is its classification as an endocrine-disrupting chemical (EDC), meaning it can interfere with the body’s hormonal systems. This chemical can mimic natural hormones, particularly estrogen, potentially impacting reproductive health and other biological processes. Concerns over this effect led to the chemical being added to regulatory lists, such as California’s Proposition 65.
The risk from sunglasses is generally considered minimal because the exposure is trace and non-dietary. Regulatory bodies have set a Maximum Allowable Dose Level (MADL) for dermal exposure from solid materials at 3 micrograms per day (µg/day). Studies estimate the upper bound for BPA dermal exposure from polycarbonate eyewear is approximately 0.53 µg per day, significantly below this threshold.
This low exposure level from solid plastics is not associated with the systemic effects seen with higher-dose dietary exposure from food containers. The consensus from risk assessments is that while BPA is present in certain eyewear, the amount transferred to the user is not significant enough to pose a meaningful health risk. Furthermore, the eye protection provided by the lenses, such as 100% UV blockage, is an undisputed health benefit that outweighs the theoretical low-level risk from residual BPA.
Selecting Safer, BPA-Free Eyewear
Consumers who wish to minimize their exposure have a variety of verified BPA-free material options.
Frame Alternatives
For frames, alternatives include cellulose-based acetate, derived from cotton and wood pulp, or bio-based nylon, sometimes made from castor beans. Metal frames, such as titanium or stainless steel, are also excellent choices for avoiding plastic components altogether.
Lens Alternatives
While polycarbonate remains popular for its safety and impact resistance, other BPA-free plastic lens options are available. These include high-index plastics and Trivex, which offer comparable durability and clarity without using BPA. When shopping, look for specific “BPA-free” labeling or ask the manufacturer to verify the exact materials used. Opting for these alternative materials eliminates even trace exposure to the chemical.