Hyaluronic acid (HA) is one of the most popular skincare ingredients in the world — and one of the most misunderstood. It's not an exfoliant. It's not an acid in the peeling sense. It's a humectant that holds water. Here's how it actually works.
What is Hyaluronic Acid?
Hyaluronic acid is a polysaccharide naturally found in the skin, connective tissue, and eyes. Its main function is to retain moisture — one gram of HA can hold up to six liters of water. In skincare, it's used as a humectant: it draws water from the environment and the deeper layers of skin toward the surface. It comes in several molecular weights, each penetrating to a different depth.
Molecular Weight Matters
High molecular weight HA (1,000–1,800 kDa): sits on top of skin, forms a moisture film, plumps instantly. Medium molecular weight: penetrates slightly deeper. Low molecular weight HA (below 50 kDa): penetrates the epidermis, supports hydration from within. Sodium hyaluronate is a salt form with smaller molecules — often more effective at skin penetration. The best products combine multiple weights for both immediate and lasting hydration.
The Most Common Mistake: Applying on Dry Skin
Hyaluronic acid needs water to work. If you apply it to completely dry skin in a dry environment, it can actually pull moisture from the deeper layers of your skin to the surface — and then that moisture evaporates, leaving skin drier than before. Always apply HA to damp skin (right after cleansing or with a facial mist) and seal it immediately with a moisturizer or face oil.
Who Benefits Most?
Almost everyone, but especially: dry and dehydrated skin (lack of water, not oil), oily skin that is actually dehydrated (common — oily skin can be low in water content), mature skin that has lost natural HA reserves with age, skin that is recovering from harsh treatments or actives. Even oily skin needs hydration — using HA often reduces the overproduction of sebum that comes from dehydration.
How to Layer It
Cleanser → toner or mist (damp skin) → apply HA serum immediately → moisturizer (to seal) → SPF in the morning. HA pairs well with everything. It complements ceramides (barrier repair + hydration), niacinamide (both address barrier function), retinol (buffers dryness), and vitamin C (reduces any dryness from ascorbic acid).
Sodium Hyaluronate vs Hyaluronic Acid
Sodium hyaluronate is the sodium salt of hyaluronic acid. It has a lower molecular weight than standard high-MW HA, is more stable in formulations, and penetrates the skin more effectively. Many high-quality products use sodium hyaluronate instead of or alongside hyaluronic acid. When reading ingredient labels, both are excellent.