Can I run 4 days after Halo with a little swelling?

It is safest to wait until your skin has healed a bit and the swelling has gone down. This should begin to happen around 2-3 days post-treatment. However, it is best to avoid prolonged exposure to the sun, so running inside on a treadmill would be advisable if possible.

I agree with Dr. Aycock that you can run, but sun protection is essential and perhaps choose early morning or later afternoon.  Drink a lot of water, moisturize and sunblock.

It is ok to run 4 days after Halo. Make sure you really moisturize your skin and apply sunblock before you go for your run. The swelling will dissipate within the next few days.