From Wikipedia:
Due to consumer confusion over the real degree and duration of protection offered, labeling restrictions are in force in several countries. In the United States in 1999 the FDA decided to institute the labelling of SPF 30+ for sunscreens offering more protection, and a similar restriction applies in Australia. This was done to discourage companies making unrealistic claims about the level of protection offered e.g "all day protection", and because an <u>SPF over 30 does not provide significantly better protection</u>.
Just a thought. Getting a good quality SPF30 > Getting a brand that's cashing in on SPF50+
Perhaps...(?)