Do you know that humans glow in the dark too?
If someone asked you to name a living thing that glows, there is a high chance you will say fireflies or glow worms. Your mind could also rush towards deep sea creatures such as jellyfish or anglerfish which are famous for their bioluminescence abilities i.e the ability to produce their own light through a chemical reaction within their bodies. Now, what if we told you that you did not really need to go that far because we human beings, all of us, glow too? Yes, albeit in extremely small quantities at levels that rise and fall during the day, we do have the same ability to glow. Let’s find out how we do it and why this light is not visible.
The body science: How do humans glow?
Actually, human bodies do emit light but it is 1,000 times less intense than the levels to which our naked eyes are sensitive. In simple terms, human bioluminescence in visible light exists, it's just too dim for our weak eyes to pick up on.
According to research conducted by Japanese scientists, the glow of human body rises and falls over the day, with its lowest point in the morning and peak in the late afternoon, dropping gradually after that. The lowest dimmest bioluminescence is observed at night. Scientists have also found out that our faces glow more than the rest of the body with the brightest spots appearing around the forehead, neck and cheeks.
This, they explain, might be because faces are more tanned than the rest of the body since they get more exposure to sunlight. The pigment behind skin colour, melanin, has fluorescent components and that could increase the body's light production.
What causes human bioluminescence?
Scientists have been able to comment on that too. In scientific terms, the glow comes from chemical reactions within our bodies. These chemical reactions besides generating energy and producing heat also produce free radicals – atoms or molecules that have a lone, isolated electron. That makes these radicals highly reactive setting off a series of energetic chemical reactions as they interact with various fats and proteins in our cells. The glow is produced when these reactions involve fluorophores – molecules that give off photons (elementary particles of light).
Since the emission levels of light produced change over the day, they believe it is linked to our body clocks or how our metabolic rhythms fluctuate over the course of the day. So, in the late afternoon when our body is burning the most energy, we glow the brightest.
Bioluminescence in animals
You can’t see the light of your own body, but if you’ve ever seen a firefly, you’ve seen bioluminescence in action. According to scientists, 76% of ocean animals are bioluminescent, including jellyfish, worms, sharks and sea stars.
How do all these animals glow? Actually, bodies of all bioluminescent animals contain a compound called luciferin which releases light when it reacts with oxygen. Believe it or not, this bioluminescence comes in very handy for these animals – it can stun their potential predator or act as a lure to draw their prey to them or warn others about the risk in the area.