Sun protection with any spray depends less on the SPF number and more on how much product actually reaches the skin. The Biosun sunscreen is a spray-lotion, so it spreads faster than a cream, but the same basic rules apply: use enough to form a visible, even film before rubbing it in, and do not rely on a light mist alone. A widely used guideline for sunscreens is about 2 mg per square centimetre of skin; in practical terms, this usually means roughly one teaspoon for the face and neck and more for the whole body—a volume similar to a shot glass. If you are applying it only to exposed arms and legs, use proportionally less, but when in doubt, apply more.
This product is described as high-protection SPF 60 with a waterproof texture, and it is meant for strong sun, outdoor sports, beach days or long walks. Waterproof does not mean the protection lasts all day; the product information states that no sunscreen stays fully intact on the skin all day. Reapply generously after swimming, sweating or towel-drying. Even without those activities, sunscreen filters gradually break down and rub off on clothing, so reapplying every couple of hours during continuous sun exposure is the normal practical approach. For a spray, this also helps ensure you did not miss areas like the back, shoulders or sides of the neck.
Because the format is quick to apply, it is easy to use more rather than less. If you are spending the whole day outdoors, keep the bottle accessible and set a reminder; high SPF can still give a false sense of security if you apply it once in the morning and forget about it.