Random Riddle: Never Down

I am something people love or hate.
I change people’s appearances and thoughts.
If a person takes care of themselves, I will go up even higher.
To some people, I will fool them. To others, I am a mystery.
Some people might want to try and hide me, but I will show.
No matter how hard people try, I will never go down.
 
Random Riddle: Never Down