When to use a sunscreen and which?

In a nutshell:

Avoid chemical sunscreens.  Some are worse that others.  Oxybenzone, avobenzone, octisalate, octocrylene, homosalate and octinoxate should all be avoided.

Use daily sunscreen on your face.  

Sunscreen should be a last resort.  Plan your outdoor time wisely.  While 10-15 minutes at noon in the sun is great for your body, 2 hours of exposure will burn you and this is when you need a sunscreen.

Never use a spray sunscreen as it can enter your lungs.

Choose a mineral based product with Titanium Dioxide or Zinc Oxide.

www.ewg.org has the sunscreen guide you need.

www.theguudcompany.com/shop has products that I love and use and are safer for you.