What is the effect of sun on bruising?

I had an upper and lower blepharoplasty and rhytidectomy 5 weeks ago. Why does my PS insist that I have to stay out of the sun COMPLETELY until the bruising has gone away? How does sun exposure affect bruising? I still have some bruising mid cheek and in my jaw and neck below and behind my ears. I use a good sunscreen and my makeup has an SPF factor of 35.