Which UV ray can penetrate the skin to the stratum corneum?

The correct choice for the question regarding which UV ray can penetrate the skin to the stratum corneum is indeed UVA rays. UVA rays have a long wavelength, which allows them to penetrate deeper into the skin compared to UVB and UVC rays. They can reach the dermis, which is just beneath the epidermis, while the stratum corneum is the outermost layer of the skin that protects against environmental damage.

UVC rays are primarily absorbed by the ozone layer and do not naturally reach the Earth's surface, making them less relevant in this context. UVB rays penetrate the skin more superficially and are primarily responsible for causing sunburn. Infrared rays, although they provide warmth and can penetrate the skin slightly, do not fall under the classification of UV rays and mainly affect the skin's thermal effects rather than causing damage or penetrating to specific skin layers like the UV rays do.

Therefore, UVA rays are recognized as the type that can reach the stratum corneum due to their ability to penetrate more deeply into the skin layers. Understanding the differences between these types of rays is crucial for effective skincare and protection against UV damage.