Are sunglasses harmful or not?

When the sun shines, many people reach for sunglasses to protect their eyes. Recently, however, an increasing number of posts have been appearing on various social media platforms that question the usefulness of sunglasses and even claim that they are harmful.
What are these claims about?
On TikTok, for example, one user explains that the eyes are equipped with receptors that signal to the body when the sun is shining and it needs to produce more melanin to protect the skin. However, if one wears sunglasses, the body would be led to believe that it is dark. Consequently, less melanin would be produced, and one would get sunburned more easily than if one did not wear sunglasses.
Is this claim true?
This statement is only partially correct. It is true that there are receptors in the eyes that register the intensity of UV radiation, but these receptors play only a minor role in controlling melanin production. The skin has its own receptors that increase melanin production in strong sunlight. This is a natural protective mechanism against damage from UV radiation. The fact that even blind people tan proves that this statement is correct.
Does wearing sunglasses interfere with the body's internal clock?
This claim is often made by people who reject sunglasses. However, it is not true. While darkness promotes the production of the sleep hormone melatonin, the body is very sensitive to light. A light intensity of just 1,000 lux is enough to convince the body that it is daytime. This corresponds to the luminosity of an 8 W LED lamp. Incidentally, this is why one should always darken the bedroom. However, commercially available sunglasses let in much more light, so melatonin production is not affected. For comparison: daylight in sunshine has a brightness of about 100,000 lux. Good sunglasses reduce the brightness to 18,000 to 7,000 lux, still more than enough not to affect melatonin production.