Hyaluronic Acid Deep Dive
Types of HA, how to layer it, and best serums by skin type and budget
Articles
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Common Questions
What is L-ascorbic acid and why does it matter?
L-ascorbic acid is the pure, active form of vitamin C that is directly usable by skin cells. It is the most researched form and offers the strongest antioxidant protection and brightening effects. However, it is also the least stable, oxidizing quickly when exposed to air, light, or heat. Formulations must include stabilizers like ferulic acid or vitamin E and be stored carefully to maintain potency.
What is ferulic acid and why is it paired with Vitamin C?
Ferulic acid is a plant-based antioxidant that significantly boosts the stability and efficacy of vitamin C and vitamin E. Studies show that combining 15% L-ascorbic acid with 0.5% ferulic acid and 1% vitamin E doubles the photoprotection of vitamin C alone and extends shelf life considerably. This trio is considered the gold-standard antioxidant combination in evidence-based skincare.
What does glycolic acid do for skin?
Glycolic acid is an AHA with the smallest molecular size, allowing it to penetrate the skin most deeply among the alpha hydroxy acids. It exfoliates dead skin cells, stimulates collagen production, reduces fine lines, fades hyperpigmentation, and improves overall skin texture. Regular use produces noticeably smoother, more radiant skin. It is best suited for normal to oily skin types as it can be drying for sensitive skin.
What is lactic acid and who should use it?
Lactic acid is a gentle AHA derived from milk that exfoliates the skin's surface while also acting as a humectant to attract moisture. Its larger molecular size means it penetrates less deeply than glycolic acid, resulting in a milder exfoliation with less risk of irritation. It is an excellent choice for dry, sensitive, or beginner skin types, and is particularly effective for improving texture and mild hyperpigmentation.
What is salicylic acid and is it only for acne?
Salicylic acid is a BHA that is oil-soluble, enabling it to penetrate pores and exfoliate from the inside out. While it is famous for treating acne by clearing blocked pores, it also reduces blackheads, controls oil, and has mild anti-inflammatory properties. It is useful for anyone with oily, congested, or combination skin, not just those with active breakouts. It can be drying at higher concentrations.
How often should I exfoliate with acids?
Most skin types do well with chemical exfoliation two to three times per week. Over-exfoliating is a common mistake that leads to a compromised skin barrier, redness, and sensitivity. If you are using a strong acid like glycolic at 10% or higher, start with once weekly and build up. Sensitive skin may do best with just once or twice a week using a gentler PHA or low-percentage lactic acid.
What is hyaluronic acid and how does it hydrate skin?
Hyaluronic acid is a humectant naturally found in the skin that can hold up to 1,000 times its weight in water. In skincare, it draws moisture from the environment and deeper skin layers to the surface, plumping and hydrating skin temporarily. For best results, apply it to damp skin before sealing with a moisturizer, as applying it to dry skin in low-humidity environments can actually draw moisture out of the skin.
What is azelaic acid and what does it treat?
Azelaic acid is a naturally occurring dicarboxylic acid found in grains that has antimicrobial, anti-inflammatory, and melanin-inhibiting properties. It effectively treats acne, rosacea, and hyperpigmentation including melasma, making it unusually versatile. It is available at 10% concentration over the counter and 15–20% by prescription. Unlike retinol or AHAs, azelaic acid is considered safe during pregnancy and is well-tolerated by sensitive skin.
Can I use acids and retinol on the same night?
It is generally not recommended to use AHA/BHA acids and retinol on the same night, especially for beginners, as the combination can cause significant irritation, redness, and barrier damage. Each ingredient increases cell turnover and used together they amplify irritation. Skin cycling addresses this by separating exfoliation night and retinol night. Advanced users with tolerant skin may use them on alternate nights but rarely the same night.
Key Terms
Vitamin C (L-Ascorbic Acid)
The most bioavailable form of topical vitamin C, acting as a potent antioxidant that neutralizes free radicals, brightens skin tone, and stabilizes collagen. Most effective at pH 2.5–3.5 and concentrations of 10–20%; highly unstable and prone to oxidation.
Glycolic Acid
The smallest alpha-hydroxy acid (AHA), derived from sugarcane, with the deepest skin penetration. It exfoliates dead surface cells, smooths texture, and stimulates collagen; effective at 5–20% in leave-on products and up to 70% in professional peels.
Salicylic Acid
A beta-hydroxy acid (BHA) that is oil-soluble, allowing it to penetrate into pores and dissolve the sebum and dead-cell buildup that cause blackheads and acne. Used at 0.5–2% in OTC products; also has anti-inflammatory properties.
Lactic Acid
A gentle AHA derived from milk that exfoliates the skin surface and has humectant properties to attract moisture. It is larger than glycolic acid, so it penetrates more slowly, making it well-suited for sensitive or dry skin types.
Azelaic Acid
A dicarboxylic acid with antibacterial, anti-inflammatory, and skin-brightening properties. Available OTC at 10% and by prescription at 15–20%, it is effective for acne, rosacea, and post-inflammatory hyperpigmentation with minimal irritation.
Mandelic Acid
A large-molecule AHA derived from almonds that exfoliates gently due to its slow penetration rate. It also has mild antibacterial properties, making it suitable for sensitive or acne-prone skin alongside addressing uneven texture and tone.
Ferulic Acid
A plant-based antioxidant that dramatically stabilizes and doubles the efficacy of vitamins C and E. It also absorbs UV radiation and reduces free-radical damage; commonly found in C+E+Ferulic serums.
Tranexamic Acid
A synthetic amino acid derivative that inhibits plasmin activity and reduces melanin synthesis, making it highly effective for melasma and post-inflammatory hyperpigmentation. Used at 2–5% topically with an excellent tolerability profile.
Kojic Acid
A byproduct of sake fermentation that inhibits tyrosinase, the enzyme responsible for melanin production. Used at 1–4% to fade dark spots and brighten skin tone; can be sensitizing for some individuals with prolonged use.
Hyaluronic Acid
A naturally occurring polysaccharide capable of holding up to 1,000 times its weight in water, drawing moisture into the skin from the environment and deeper layers. Available in multiple molecular weights; lower weights penetrate more deeply, while higher weights sit on the surface.
Polyglutamic Acid
A fermentation-derived polymer with four times the moisture-holding capacity of hyaluronic acid, forming a film on the skin's surface to lock in hydration. It also inhibits hyaluronidase, the enzyme that breaks down the skin's natural hyaluronic acid.