What is the difference between SPF 50 and SPF 50+?

There is no major difference in terms of protection between SPF 50 and SPF 50+. In fact, it might give you a false sense of security to choose a high SPF in the belief that it will give you extra protection. Actually, it is much more important that you apply the right amount of sun screen. If you apply too little sun screen using a significantly lower SPF, your UV
protection will be significantly impaired.

Sun screens with protection in the range of 50 to 59.9 are designated at SPF 50. Protection of over 60 calls for SPF 50+.

How much the sun screen blocks the sun's harmful rays:

SPF 50: 98.0%
SPF 50+: 98.3%

So the difference between the two is minimal.