Why does outside feel like outside?

You walk outside, you take a breath of fresh air. It smells different. It feels different. Why?

Is it the fact that the air is moving? Is it the plants? Is it the fact that homeostasis becomes easier because air is moving?

Is it the feeling that you can see the sky?

For me, a day always feels better when I’ve been able to get outside. I’m sure some of it is the sun, as getting outside during the day is better than at night, but even getting outside at night feels better than being inside.

So, what could it possibly be? Let’s go over the options:

1) Light

As anyone who’s ever used a full-spectrum light box knows, they can be incredibly powerful and useful in changing one’s mood and awakeness state. There could also be something to do with Vitamin D, even a placebo effect during the winter. (It is suggested that the human need for sunlight-created Vitamin D might be sufficient to explain much of the variation of human skin colour.)

2) Something in the air

Something about the outside just feels fresher. I don’t think inside air really has concentrations of CO2 or O2 that much different from that outside (if it really built up that quickly, you would probably suffocate), but there might be other impurities either missing or in higher concentrations inside.

3) …or something in the way it moves…

If you’ve ever seen a cat react to a window being opened on the other side of the apartment, you know that they can detect air currents. I know that I love the breeze on my face (at least during the non-winter).

4) Sounds

The rustling of leaves, the chirping of birds. They make me feel more relaxed. Like I’ve come out of my cave and I’m alive again? Even the sound of the wind…

5) Not having something overhead

Again with leaving the cave. There’s something uniquely oppressive about having something overhead that close all the time. It makes you feel like you’re hiding all the time? So, why do trees not trigger any fear of something jumping out of them at you? Have humans been apex predators that long? Or is it something that is trained into you, like hearing Lancasters flying overhead?