Yes tanning beds are more harmful for your skin and health than the sun is.
When you tan in a tanning bed you're closely exposed to those very strong and harsh UV or Ultraviolet Rays that give your skin the tan.
Tanning in a tanning bed you're more at risk for developing skin cancer than you would when tanning outside in the natural sunlight.
If you do want to use a tanning bed for tanning your skin you should avoid going to the tanning bed too often to prevent the possibility of getting skin cancer.
Use the tanning bed in moderation and not too often.
I would not go to a tanning bed more than once per week or maybe just go to the tanning bed twice per month at most.