According to the American Cancer Society approximately 5.4 million basal and squamous cell skin cancers are diagnosed each year. Yet, the sun does contribute to the production of Vitamin D, which is necessary for bone health, and perhaps even useful in preventing some cancers. So how does one know how much sun exposure is enough?

Andrea M Armani, the Fluor Early Career Chair and Associate Professor and doctoral candidate Michele E. Lee in the Mork Family Department of Chemical Engineering and Materials Science at the USC Viterbi School of Engineering have developed a color-changing wearable that can notify users of their total exposure, allowing them to achieve a balance.

A user wears the 0.5" by 0.5" millimeter sized flexible patch and is notified of total UV exposure by the change in color. When the sensor turns orange, the user has reached the World Health Organization recommended daily dose of Vitamin D.

Because the sensor patch is less than half a millimeter thick and is extremely flexible, it is ideal for outdoor enthusiasts and athletes. Unlike app predecessors on the iPhone or Samsung watch, it does not require a power source. In addition, the sensors created by the Armani Lab, still work when wet and will function and adjust their responses when sunscreen is applied.

Furthermore, the sensors can be stored for a period of up to five weeks. These sensors are made of material patented by Armani and Lee and were constructed of FDA-approved non-toxic polymers for human use and food contact.

Their innovation is documented in "Flexible UV Exposure Sensor Based on UV Responsive Polymer," in the journal ACS Sensors.

Researchers Armani and Lee indicate that this sensor addresses the unique challenges of trying to gauge sun exposure in the face of the varying geographical and environmental influences as well as the bio-chemical make-up of individual users.

In the future, the researchers can adjust sensor performance and optimize the sensors for different skin types through the use of additional coatings and tailoring of the color-changing active layer.