Is it true that once a suncream is opened the SP factor of it starts to diminish?

I have heard that if you re open a suncream a year later (for your next holiday) that the SP factor would have gone down eg? factor 50 becomes factor 40?!!

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Patty Inglish, MS profile image90

Patty Inglish (Patty Inglish, MS) says

5 years ago
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