Understanding Sun Protection

There are two types of sunscreen.  Chemical and Physical.  Chemical screens ABSORB the sun's rays while physical ones REFLECT the rays.

Physical sunscreens:

• titanium dioxide
• zinc oxide 

Chemical sunscreens:

• octinoxate (octyl methoxycinnimate)
• octisalate (octyl salicylate)
• oxybenzone (benzophenone)

What is SPF?  SPF stands for Sun Protection Factor which was developed by scientists who were studying physical sun damage in 15 minute increments.  In order to better understand what those numbers mean on your sunscreen bottle there is a formula which can be followed to estimate how long your sunscreen can protect you.  This applies to both physical and chemical sunscreens.

Say you have a sunscreen with an SPF of 4:

SPF 4 X 15 minutes = 1 hour
60 minutes

Other examples:
SPF 8 X 15 minutes = 2 hours
60 minutes

SPF 15 X 15 minutes = 3.75 hours
60 minutes

SPF 35 X 15 minutes = 8.75 hours
60 minutes

SPF 45 X 15 minutes = 11.25 hours
60 minutes

SPF 50 X 15 minutes = 12.5 hours
60 minutes

And so on, but remember even though an SPF of 50 MAY protect for up to 12.5 hours other factors such as sweat and swimming will the time it is effective to plan accordingly and re-apply liberally if you are playing in the sun.

28 June 2019- Edit to add.

Over the years I learned a few more things about sun protection and thought I would share it here. First, sunscreen has a job, it's job is to protect you from sunburn and the harm that comes with it. Because it has a job and you need to know it can do its job sunscreen must go through testing and approval by the FDA, it is technically considered a "drug". The process of getting an item tested and approved through the FDA is very costly and not something most home makers can afford to do. PLEASE, PLEASE, PLEASE always buy sunscreen that has been FDA approved. By doing so you know that it will work as it claims to and will keep you protected and safe. 

Stay safe my friends
~your Soapsmith