Can a face serum with SPF replace sunscreen?

What should an SPF serum's label say?

SPF describes protection against sunburn, primarily from UVB rays. Broad spectrum adds protection against UVA rays. A higher SPF, up to 50, provides greater sunburn protection, but SPF is not a timer: SPF 30 does not mean you can spend 30 times longer in the sun. The amount applied, sun intensity, swimming and sweating all affect protection.24

How do you apply a face serum with SPF?

1. 1Read the particular product's sunscreen directions. For layering, follow any instructions on that label rather than assuming the word "serum" determines its place in your routine.
2. 2Apply sunscreen at least 15 minutes before going outdoors.
3. 3Apply generously and evenly. For the face, the American Academy of Dermatology advises at least 1 teaspoon, roughly enough to cover the length of your index and middle fingers. Rub it thoroughly into your skin.
4. 4Cover other exposed skin too, including your neck, ears and hairline. Keep sunscreen out of your eyes and mouth, and use an SPF lip balm for your lips.
5. 5Reapply every two hours while outdoors, and immediately after swimming or sweating. Reapply after towelling off too.

Applying less than the recommended amount greatly reduces protection. If you only want to use a small amount of serum, use a separate sunscreen in its full recommended amount instead of counting that small serum application as your sun protection.2

When do you need it?

Use sunscreen before going outside, including on cloudy days and in winter. A morning application does not remove the need to reapply during outdoor exposure later in the day. Water resistant sunscreen still washes off eventually; no sunscreen is waterproof. Follow the water resistance time and reapplication directions on the product rather than treating a water resistant label as all day coverage.14

What can you expect from an SPF serum?

Correctly used sunscreen helps prevent sunburn and protects against premature skin aging and skin cancer. For concerns about dark spots, a tinted sunscreen containing iron oxide also protects against the sun's visible light. The SPF number describes sun protection, not how quickly a serum will improve an existing skin concern.14

The UV filtering active ingredients provide the sun protection; other ingredients make up the rest of the formula. Compare the actual sunscreen label before deciding whether a serum format meets your needs.4

What if your skin is sensitive or prone to breakouts?

Before using a new SPF product, test it on a small area of your inner forearm and check for a reaction after 48 hours, especially if your skin is sensitive. If you develop a rash, itching or another reaction, stop using that product and try a different type or brand. Sunscreen reactions are rare, but sensitivity or allergy can involve UV filters, fragrances or preservatives. Ask a health care professional about a reaction or a known ingredient allergy.2

For skin prone to breakouts, look for products labelled noncomedogenic, meaning intended not to clog pores. Labels can also say "oil free" or "won't clog pores." If a rash or other skin problem lingers or worsens, contact a dermatologist.5

Do medicines change the advice?

Some medicines can cause an allergic reaction when skin is exposed to sunlight, including doxycycline, tetracycline and minocycline. Check your medication container or ask your pharmacist. If your medicine can cause this reaction, stay out of the sun rather than relying on an SPF serum alone. Seek shade and wear protective clothing, a wide brimmed hat and sunglasses alongside sunscreen.5

How should you store it?

Keep your SPF product out of direct sunlight and high heat, including a hot car, because extreme heat can reduce sunscreen effectiveness. Do not use expired sunscreen. In the US, a sunscreen without an expiry date should be considered expired three years after purchase; discard it if you do not know how old it is.24