Lactic Acid: A Gentle AHA for Dry and Sensitive Skin

What is lactic acid, and what role does it play in cosmetics?

Lactic acid is an alpha-hydroxy acid (AHA) naturally found in milk, fermented dairy products, and certain fruits. Produced through the bacterial fermentation of glucose, it is now widely used in cosmetics for its gentle exfoliating, moisturizing, and skin-soothing properties.

When applied topically, lactic acid helps loosen surface cells in the stratum corneum, contributing to a smoother skin texture and a more even-looking complexion. Compared to other AHAs, it is distinguished by a larger molecular size, which limits its penetration into the skin and improves its tolerability. It is primarily valued for:

• Skin hydration: It helps attract and retain water in the superficial layers of the epidermis.
• Complexion radiance: It promotes a more luminous-looking complexion and helps visually even out skin tone.
• The appearance of signs of aging: It helps minimize the appearance of fine lines caused by dehydration and visually smooth the skin.
• Skin with superficial imperfections: It gently supports skin seeking to refine its texture.

What are the benefits of lactic acid for the skin?

Lactic acid is suitable for most skin types, particularly dry, dull skin or skin with superficial imperfections. Its main cosmetic benefits:

1. Gentle exfoliation: It helps remove dead surface cells with better tolerance than most other AHAs.
2. A more even complexion: It helps visually reduce the appearance of post-breakout marks and skin tone irregularities.
3. Smoother skin texture: It refines the appearance of theskin’s texture and leaves the skin feeling soft.
4. Supports surface renewal: It supports the natural renewal process of the stratum corneum.
5. Enhanced hydration: It helps maintain hydration and promote skin comfort.

Claims regarding the stimulation of dermal collagen by cosmetic lactic acid should be qualified: at cosmetic concentrations and the product’s pH, the primary action remains superficial. For pronounced pigmentation spots, severe acne scars, or significant signs of aging, a dermatological consultation can help guide you toward appropriate solutions.

Is lactic acid suitable for sensitive skin?

Yes, lactic acid is one of the best-tolerated AHAs, even for sensitive and reactive skin. Its larger molecular size limits its penetration and thus the risk of irritation. However, several precautions are essential before incorporating it into a skincare routine:

• Start with a low concentration (around 5%) and increase gradually if necessary.
• Use the product no more than 2 to 3 times a week for the first few weeks.
• Always apply sunscreen with an SPF of at least 30 during the day—lactic acid causes skin photosensitivity.
• Avoid combining it with other exfoliating or irritating active ingredients (retinol, other AHAs, BHAs, pure vitamin C) during the first few uses.
• Perform a tolerance test on the inner elbow for 48 hours before the first application to the face.

If you have atopic, couperose, rosacea-prone, or highly reactive skin, cosmetic lactic acid should only be used after consulting a dermatologist.

How can you incorporate lactic acid into your skincare routine?

Lactic acid comes in various cosmetic forms: serums, creams, toners, and exfoliating masks. Typical cosmetic concentrations range from 2% to 10%. Concentrations higher than this fall into the category of supervised chemical peels, which should only be performed by a professional.

• Dry and sensitive skin → opt for a serum or moisturizer with a maximum concentration of 5%, used 1 to 2 times a week in the evening.
• Normal to combination skin → opt for a serum or lotion with 5–8%, 2 to 3 times a week in the evening.
• Dull or uneven skin tone → Follow a gradual routine with a 5–10% serum, combined with thorough moisturization.
• Skin with superficial blemishes → Opt for a gentle, gradual approach, and consider combining it with a BHA on an alternating basis rather than using them together.

Practical tips: Apply in the evening to clean, dry skin; wait a few minutes before following with a moisturizer; and always use broad-spectrum sunscreen in the morning.

Lactic Acid vs. Glycolic Acid: What Are the Differences?

Lactic acid andglycolic acid both belong to the AHA family but have significant differences:

Compared tosalicylic acid (a fat-soluble BHA), lactic acid is a water-soluble AHA: it acts on the skin’s surface, whereas BHA acts deep within the sebaceous pores. The two are complementary but should not be used on the same night to avoid cumulative irritation.

Which one should you choose?

• Sensitive, dry, or dehydrated skin → opt forlactic acid.
• Normal to combination skin seeking a more pronounced exfoliating effect →glycolic acid may be considered once your skin has adjusted to it.
• Oily, acne-prone skin with visible pores → salicylic acid (BHA) is often a better choice.

Is lactic acid found in food?

Yes, lactic acid is naturally produced during the lactic fermentation of many foods:

• Yogurts, fresh cheeses, and fermented milks.
• Kefir, kombucha, sauerkraut, and kimchi.
• Apple cider vinegar, pickles, and certain lacto-fermented vegetables.

In the diet, lactic acid itself is not a probiotic: it is the live lactic acid bacteria present in unpasteurized fermented products that can help maintain the balance of the gut flora. A varied and balanced diet that includes high-quality fermented foods generally supports digestive comfort. For any persistent digestive issues, medical advice is recommended.

What are the side effects of lactic acid?

Lactic acid is generally well tolerated at typical cosmetic concentrations. However, several adverse effects may occur if used improperly:

• Redness, tingling, and a sensation of warmth, especially when first used or at concentrations that are too high.
• Photosensitivity: increased skin sensitivity to UV rays, with a higher risk of hyperpigmentation if sunscreen is not used consistently.
• Dryness and tightness if applied too frequently.
• Superficial peeling during the first few weeks, which should remain mild.
• Allergic reactions are rare but possible.

To minimize these effects: introduce gradually, start with a low concentration, moisturize consistently after application, avoid combining chemical exfoliants, and apply sunscreen during the day. Special precautions: During pregnancy and breastfeeding, medical advice is recommended before introducing an AHA into your skincare routine, even at low concentrations. A widespread reaction (severe redness, itching, swelling) requires discontinuing the product. A systemic reaction (facial swelling, difficulty breathing) requires calling 15 or 112.