Glossary
SPF vs PA
SPF measures UVB. PA measures UVA — the range linked to pigmentation. You need both numbers.
Sunlight reaches skin as two ranges of ultraviolet, and a sunscreen label tells you about each with a different number.
SPF measures protection against UVB — the range that burns. SPF 30 filters about 97% of UVB; SPF 50 about 98%. The jump from 30 to 50 is small on paper and still worth having, because almost nobody applies enough to achieve the stated figure.
PA measures protection against UVA — the range that penetrates deeper, passes through window glass, and is associated with pigmentation and long-term change. It is written as PA+ to PA++++, with four plusses the highest. European products often use a UVA inside a circle instead, which means the UVA protection is at least a third of the SPF.
For Bangladesh, look for SPF 50 with PA++++, or SPF 50 with the circled UVA mark. An SPF number on its own tells you nothing about the range most relevant to dark spots.
Amount matters more than either number: roughly two finger-lengths for face and neck. Half the amount is far less than half the protection.
See also
This article is general information, not medical advice. Skincare products are not medicines. Speak to a dermatologist about persistent or worsening skin conditions.