What is the difference between a serum and a moisturizer?

A serum and a moisturizer are both essential components of a skincare routine, but they serve different purposes and have distinct textures, ingredients, and functions.

What is a Serum?

A serum is a lightweight, fast-absorbing liquid or gel that contains a high concentration of active ingredients. It is designed to penetrate deeply into the skin and target specific skin concerns such as fine lines, wrinkles, dark spots, acne, dehydration, or dullness. Serums often contain potent ingredients like vitamin C, hyaluronic acid, retinol, peptides, niacinamide, or antioxidants.

Because of their smaller molecular structure, serums can deliver active ingredients more efficiently than moisturizers. They are usually water-based or sometimes oil-based, but either way, they do not typically contain the thick emollients or occlusives found in moisturizers.

Serums are applied after cleansing and toning, but before moisturizing. Their role is to treat the skin, not to seal in moisture.

What is a Moisturizer?

A moisturizer is a cream, lotion, or gel that is designed to hydrate the skin and lock in moisture. It helps strengthen the skin’s barrier, preventing water loss and protecting it from external irritants like pollution or dry air. Moisturizers contain ingredients such as humectants (e.g., glycerin, hyaluronic acid), emollients (e.g., squalane, ceramides), and occlusives (e.g., petrolatum, dimethicone) that work together to keep the skin soft, smooth, and supple.

While moisturizers may contain some active ingredients, their main job is to provide hydration and maintain the skin’s moisture balance. They are applied as the last step in a basic skincare routine to seal in everything underneath.

Key Differences

Do You Need Both?

In most cases, yes—especially if you have specific skin concerns. Serums provide the targeted treatment, and moisturizers help lock those benefits in. Using only a serum may leave your skin dehydrated, as it doesn't provide the occlusive layer needed to prevent moisture loss. Using only a moisturizer might hydrate your skin, but it won’t address deeper issues like pigmentation or collagen loss as effectively as a serum would.

Final Thoughts

Think of a serum as a treatment and a moisturizer as protection. Serums are packed with actives to address your skin’s needs at a deeper level, while moisturizers maintain the skin’s barrier and keep it nourished and hydrated. For best results, combine both in your routine: apply your serum after cleansing and toning, and follow up with a moisturizer to seal in all the benefits. This combination helps keep your skin healthy, glowing, and well-balanced.