suncream and glass

[veritysims]

Do UV rays penetrate glass. I put suncream on my children on very sunny days even if we are just in the car but my mum says that uv rays bounce off glass and you only need suncream outside. my cousin swears he gets sunburnt arms in the summer when he drives alot.

[gen2]

The short answer is that UV light is divided into UVA and UVB.  Window glass almost completely blocks the more damaging UVB but still lets the UVA through.  This can still produce a tan and is emitted by the lamps in tanning studios.  UVA is also considered damaging by many experts.

When using sunscreen lotions, the sun protection factor (SPF) is based just on protection against UVB, but many products also claim to offer protection against UVA.

More details are given on these sites

This site tells us: 

Light in the UVA range has wavelengths of 320 to 400 nm, while UVB waves are 290 to 320 nm in length. Sunburns are caused primarily by UVB radiation. UVA rays penetrate more deeply than UVB, and contribute to premature aging of the skin. Both UVA and UVB rays cause skin cancer.

and this site tells us: 

Characteristics of UV Radiation

UV-A
Same intensity all day 
Intensity is similar all year round 
Intensity is similar for all locations bewteen the two poles 
Penetrates glass & plastic

UV-B
Higher intensity between 10am and 2pm
Intensity is lower in winter months
Intensity is greatest close to the equator and least at the poles
Does not penetrate glass & plastic

NB
UV-B light is blocked almost completely by a single pane of window glass, but UV-A passes through even tinted window glass easily.

[veritysims]

great answer - very informative. I will continue to use suncream on the kids when in the car. Thanks