SPF literally translates as - Sun Protection Factor (sun protection factor). The higher its value, the stronger the protection. Let me explain now. Creams with an SPF of up to 15 are suitable for everyday use in the city during the hot season (the condition is inconsistent exposure to the sun). For example, if a person in his hometown only moves from home to work, takes short walks ...
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The main superpower of SPF creams lies in physical or chemical filters.
Creams based on physical (or mineral) filters reflect UVA and UVB rays. Particles of minerals act as a reflective shield, glare in the sun, and do not penetrate the epidermis.
Two types of physical filters are most often used:
✔️ zinc oxide (found on jars as Zinc Oxide) - an inorganic mineral compound, has broad spectrum protection and reduces the production of free radicals in the deep layers of the skin. Does not absorb into the skin, blocks UVA and UVB rays
✔️ Titanium Dioxide - a chalk mineral with high reflectivity. Does not irritate the skin, does not cause allergies, does not contribute to the formation of comedones. Protects from UVB rays and partly from UVA radiation
Chemical filters work differently. Creams based on them absorb the sun's rays - chemicals penetrate the surface layer of the skin and convert solar radiation into safe thermal energy. These filters work great even at low concentrations with an SPF below 20. But not all of them are effective against UVA rays. Therefore, chemical UV filters are often combined with each other or with physical filters.
Creams with chemical filters start working 20 minutes after application, so this should be done in advance before going out, and also reapplied if you bathed or sweating a lot.
Interested in the mechanism of action.