Consumer Wearables – A Model for Mitigating ACD Risk

Consumer wearables are part of the smart device market, and they have some of the same issues that the other smart products have throughout their lifecycle. “One of the issues is there isn’t much guidance, and there’s even less regulation,” said Patrick Sheehan, principal scientist at Exponent, during a presentation at Product Stewardship 2017.

What makes wearables different from other electronic products is that they’re made to be worn close to the skin for extended periods of time under conditions where there might be sweat from exercise or water from showers. And those conditions, create an environment conducive to the leaching of chemicals and the uptake of the leached chemicals into the skin.

For these reasons, biocompatibility is the unique aspect that needs to be considered by the product stewards, said Sheehan.

Though the most obvious products are related to exercise monitoring, wearables are also widespread in health care and the entertainment markets, with things like Augmented Reality headsets, smart glasses and more. Wearables have also found applications in military and industrial markets.

To properly evaluate wearable products, product stewards have to consider risks such as allergic contact dermatitis, irritation, electric shock or burn due to battery corrosion, mold and odor development, and security of user data. “When we look at these challenges, the one that really comes to the forefront is allergic contact dermatitis (ACD),” said Sheehan.

Allergic Contact Dermatitis and Risk

Allergic Contact Dermatitis (ACD) reactions are both visible, in the form of rashes, and potentially painful. A variety of materials go into wearables – metals, polymers, adhesives – and they all have the possibility of containing a sensitizing chemical. And due to the manufacturing process, they may not be fully bound and therefore available to be released when the consumer wears the product.

When consumers have a reaction caused by a wearable, they are likely to share with their friends and social networks, causing a potential public relations problem for the manufacturer. Manufacturers should also be concerned about litigation and liability, said Sheehan.

Estimating risk for ACD is challenging because the body goes through a two-step process. In step 1, the body is sensitized, and there may not be a visible reaction. After sensitization, the next time the body is exposed to the chemical, it reacts with inflamed skin and other typical symptoms.

Consumers could potentially have a reaction to a wearable without being sensitized by the device itself, said Sheehan. For example, people are sensitized to nickel because of jewelry, and after they’re sensitized, they are susceptible to eliciting reactions from the device.

A tool called the Local Lymph Node Assay (LLNA), provides data that gives an impression of the likelihood that a chemical at a certain level will cause a reaction. Not much attention is paid to this part of the process, said Sheehan: “That’s why the focus has been primarily on the elicitation end, the second phase of the process.”

There are some clinical tests that provide data sets to help evaluate exposure and response. Some models have been used for a few metal sensitizers. They’re not set up to give a total evaluation of risk, however.

Evaluating ACD Elicitation

Ankur Singh, managing scientist at Exponent, shared the company’s process for evaluating ACD elicitation risk. The first thing they do is characterize a representative exposure scenario that reflects real life. The test-design phase is critical. Singh cautioned that out-of-box testing protocols won’t work for wearable products. Instead, each test must be specific to the product.

As far as the tests go, you can conduct leaching experiments, where you fully immerse the product in artificial sweat solution, with modifications based on duration, temperature, and shaking. For some products, if you leave the device in water longer than eight hours, the seals will be compromised and water will ingress into the electronics, Singh noted, so this test doesn’t work for all devices.

An alternate method is the “Conduct Transfer Test” based on a surface transfer experiment. In this test, you wrap the device in artificial sweat-wetted wipes. The method is less aggressive then the leaching, but is also more representative of end-use scenarios, said Singh.

Following the tests, you submit the leachate or wipes to a lab, which returns a list of chemicals that migrated from the device. The next step is to identify the sensitizers on the list and calculate the dermal load, which Singh described as the “mass of sensitizer released divided by relevant area of skin that comes in contact with device.”

The final step for Exponent is to input this information into a custom model to estimate the percentage of the sensitized population that will have ACD reactions.

Using nickel as a reference point (because of the data available), the model scales chemicals for which there is not much data available, allowing the company to evaluate the relative potency and estimate ACD risk.

The Most Important Question

Now that you have a number, what do you do when there’s no guidance or regulation around appropriate risk? One option is to try and remove all the sensitizing chemicals from the product. If that’s infeasible, another option is to modify manufacturing processes to ensure that adhesives are fully cured or that the device is coated. Ultimately, what to do is a business decision, based on what your company considers an acceptable risk.


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