Serums are concentrated formulas designed to sink into skin quickly. You generally need only a few drops to cover the face, a practical limit to the bottle's ambitions. Serum performance depends on its active ingredients, formulation, vehicle and stability, so check the ingredient list for the job you want it to do.1

What does a hydrating serum do?

Humectants such as glycerin and urea attract and retain water in the stratum corneum, the outermost layer of skin. Hyaluronic acid also retains water and is used in skin serums. These ingredients support water retention; the finished serum's performance depends on its formula.234

A moisturizer can combine humectants with emollients, which soften and smooth skin, and occlusives, which form an oily barrier that reduces water loss. Those ingredients have different jobs: attracting water is not the same as slowing its evaporation. Ingredient choice matters more than price, so the product name does not get to chair the meeting.123

Who should use a hydrating serum?

If your skin feels dry, tight or flaky, a serum with hyaluronic acid is one option to consider. Ceramides are another ingredient to look for because they help keep moisture from escaping. The exact result still depends on the product's formula, not just the name on the bottle.1

Sensitive skin can react to powerful serum ingredients. Test a small area before applying a new serum widely, and introduce one new product at a time. Use caution when combining acid containing serums with other products that contain acids, or when pairing a vitamin C serum with retinol cream or a retinol serum with prescription retinol cream. If skin irritation or contact dermatitis, a product related skin reaction, appears, stop using the serum and make an appointment with a dermatologist.15

For a serum containing hyaluronic acid, Cleveland Clinic describes hyaluronic acid as safe during pregnancy and nursing. That statement applies to hyaluronic acid, not automatically to every other active ingredient in a blended serum.4

Can a hydrating serum replace moisturizer?

Do not assume it can. Serums and moisturizers are different product categories, and moisturizers can include ingredients that soften skin or reduce water loss. If you want to add a humectant step, apply the serum before moisturizer rather than treating it as an automatic replacement.12

How do you apply a hydrating serum?

  1. 1Cleanse gently and pat your face dry.
  2. 2If you use prescribed skin medication or another treatment, apply it immediately after cleansing and follow its directions.
  3. 3Apply the serum to clean skin after cleansing and before moisturizer. A few drops are usually enough for the face.
  4. 4Apply moisturizer after the serum to help reduce water loss.
  5. 5In the morning, finish with sunscreen. At night, leave sunscreen out.
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A straightforward morning routine is cleanser, serum, moisturizer and sunscreen, in that order. In the evening, put serum after cleansing and before moisturizer. Keep the routine simple: using several new products at once raises the chance of irritation, and your face did not ask to host a committee.5

Where this answer comes from

  1. 1Skin serum: What it can and can’t dohealth.harvard.edu
  2. 2Emollients and Moisturizers (Moisturisers)dermnetnz.org
  3. 3Moisturizers: Do they work?health.harvard.edu
  4. 4Hyaluronic Acid: What It Is, Benefits, How To Use & Side Effectsmy.clevelandclinic.org
  5. 5The Correct Order for Skin Care Productshealth.clevelandclinic.org
  6. 6Should I apply my skin care products in a certain order?aad.org