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How many SPF values do suntan lotions lose in the year between summer holidays?
For example, if I buy SPF20 today for a holiday, and have some left, what SPF will it have next December if I decide to go on holiday again?
asked in suntan lotion, chemistry

imfeduptoo answers:

If it is still within it's sell-by date it will have the same amount of protection; according to Cancerhelp UK sun creams can last 2 to 3 years, so if it hasn't gone rancid or out of date it will still give you the same protection.


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seacommander answers:

One of our hospital pharmacists says that a rule of thumb for active ingredient degredation after the expiry date is 5% per month. So, in a little over 1 year the SPF may have fallen to about half of the original value.

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