Using sunscreen reduces the body's production of vitamin D, a potent anti-cancer agent:

http://greathealinggetaways.com/Sunscreenarticle.html

Sunscreens often contain carcinogens:

http://en.wikipedia.org/wiki/Potential_health_risks_of_sunsc...

Consequently staying indoors and using sunscreen may _increase_ your likelihood of developing cancer.

Children who avoid sunshine will get rickets, a disease that was once almost absent from the US population:

http://www.telegraph.co.uk/health/healthnews/8128781/Middle-...

Nonetheless, the fair-skinned must balance their exposure carefully. Good news is that their skin produces vitamin D more efficiently than darker skin, so the fair-skinned can obtain vitamin D in a shorter exposure period (minutes a day):

http://www.usatoday.com/news/health/painter/2009-04-19-your-...