The Old Testament even references the healing properties of humor: "A merry heart doeth good like a medicine." Although Jews know intuitively about humor...(believe me, we've have had a lot of experience over the centuries with number four)
Well now we know a few things scientifically.
According to Maud Purcell (LCSW, CEAP) in her article The Healing Power of Humor
Humour does many things:
1) Reduces pain--Our bodies produce pain-killing hormones called endorphins in response to laughter.
2) Strengthens immune function -- A good belly laugh increases production of T-cells, interferon and immune proteins called globulins.
3) Decreases stress--When under stress, we produce a hormone called cortisol. Laughter significantly lowers cortisol levels and returns the body to a more relaxed state.
4) Helps put life's trials and tribulations into healthy perspective by making them seem smaller.
5) Aids us in overcoming fear.
6) Allows us to take ourselves less seriously.
7) Triggers our creativity.
Ms. Purcell goes on to say, "You have a choice: You can continue to be a 'grown-up,' and let all of the frustrations and disappointments in life weigh you down, or you can introduce levity into even the toughest circumstances. "