Why do you feel more tired when sunburnt?



Why do you feel more tired when sunburnt?

In: Biology

Because your body is spending energy trying to heal you. Also swimming is both good exercise and an efficient way to get sunburnt so that may also play a role

“Sunburn” is another name for “nuclear radiation damage to millions of cells across a wide area of the body”.

1. There is a flurry of activity by DNA-repair enzymes and other repair processes.
2. Those cells with irreparable damage sense it and commit mass cell-suicide to avoid becoming cancer. Their “bodies” then need to be swept up and taken away.

All together, that is a massive drain on your immune system and body energy stores. And at the same time, being sunburnt probably means you were outside a long time – which means you’re likely dehydrated and maybe muscle fatigued from hiking, swimming etc. Add all that to the radiation damage and it’s no wonder you’re wiped.


Edit: I didn’t mean alpha/beta/gamma radiation, it’s solar UV (*electromagnetic* radiation from a nuclear explosion) that causes sunburn.

The Sun emits a ton of light particles. Each particle has a different amount of energy, some having enough energy to hurt your cells causing sunburn. The one’s that cause Sunburn fall under UV (ultraviolet).

When your skin cells absorb this UV light, it breaks apart the structures of these cells. Your body needs to remove this damage and get rid of them. Like any damage your body processes, your skin undergoes inflammation from your damage by the repair cells coming to clean up.

When you have a sunburn, you have millions of these tiny damages invoking a very large immune response causing massive amount of inflammation and raising your body temperature. This amount of work is tremendous and makes you tired. Also, the clean up chemicals the cells make to repair/protect you also make you tired and not feel well.

You literally have a burn across a large portion of your body. Sometime causing a second degree burn meaning it penetrated the outer layers of your skin to the under layers that are more sensitive to damage. Just like in fighting off an infection if your body is working overtime to repair that much damage it’s going to prioritize energy stores to the cells that need it most.

Damage detected on skin surface from prolonged contact with sun rays.

Execute healing and cleanup initiatives to repair damage.

Notice: healing requires resources, this process may cause light fatigue.

Because your body is using all its energy/calories trying to repair the damage you allowed the sun to do

Another factor apart from what everyone has said about skin damage is that you’re also likely to become dehydrated

You are not just “burned”, the largest organ of your body (the skin) is having widespread inflammatory response to recover from the burn damage.

Inflammatory response is when the immune system is hard at work, and it’s pretty much the same mechanism that makes you feel tired when you are unwell from other causes.

Sunburn is an injury to your skin. When your body repairs itself it diverts resources to that task, causing you to feel tired.


If you really want to be mind blown, getting large tattoos feels much the same, both in skin pain at the tattoo site, and the drained tiredness and malaise I associate with sunburn.

In fact, some even call the reaction “tattoo flu”. Similar thing though, I imagine. Damage to the body, trauma, mild shock, inflammation responses, etc.

Will spf help prevent this if I’m also hydrated?

Similarly, can someone explain the science behind why I’m so tired after a tattoo?

Likely due to the dehydration and whatever you were doing that caused you to be sunburned. Plus, that’s a large surface area burn, and especially if it’s peeling off, that’s a lot of water loss from the burned areas of skin.

Sunburns kill skin cells, causing an acute increase in proteins called interferons (among others). These are proteins that have many roles including anti viral effects. A known effect of interferons that are given therapeutically is extreme fatigue (used to be given in cases of hepatitis infection). Source – I am a dermatologist/immunologist.