What is citric acid used for in scalp care products?

A common ingredient in kitchen pantries and fizzy drinks, citric acid might not be the first thing that comes to mind when thinking about scalp care. Yet, this mild organic acid plays an essential role in many hair and scalp formulations. But what exactly does it do? Why is it added to the shampoos, conditioners, and scalp treatments that line drugstore shelves? Let’s dive deep into the science-backed reasons that make citric acid a valuable ally for scalp health.

What Citric Acid Actually Does for Your Scalp

When you see “citric acid” on the label of a shampoo, conditioner, or scalp treatment, it’s not there by accident. This mild organic acid—widely known from lemons—is doing important work, both scientifically and within the beauty industry. so,

Your scalp’s ideal pH is slightly acidic, around 4.5–5.5. This acidity supports a healthy skin barrier and controls unwanted bacteria and fungi. But many hair products are too alkaline, which can disrupt that balance and cause dryness or irritation. Citric acid gently lowers the pH of these formulas to match the scalp’s natural environment. This isn’t just a marketing claim—its buffering role is confirmed by ingredient databases like Incidecoder, which identify buffering and pH-regulating as its primary functions.

Cutting Through Hard Water Build-Up

If your water is hard (high in calcium or magnesium), minerals can stick to your scalp and hair, making them feel dull or look flaky. Citric acid acts as a chelating agent, binding those minerals and rinsing them away so products work properly. A June 2025 study published in the International Journal of Cosmetic Science tested citric acid on chemically treated hair. Results showed that citric acid lowered calcium levels by around 21–42% and strengthened treated hair by improving its internal bonding. This suggests it helps detoxify hard-water minerals on the scalp.

Reinforcing Hair That’s Been Chemically Treated

That 2025 study also revealed structural improvements in chemically treated hair—up to 23% stronger tensile strength and almost double resistance to fatigue. While this study focused on hair shafts rather than the scalp directly, it shows citric acid supports the protein structure exposed at the scalp when treatments like bleaching naturally weaken hair.

When Too Much Can Be Harmful

It’s worth noting that citric acid isn’t always harmless. A 2022 animal and cell study found that injecting citric acid suppressed hair growth, caused inflammation, and triggered cell damage in mice and cultured human hair follicles. While this method doesn’t reflect normal cosmetic use (where it’s applied topically at low concentrations), it highlights the importance of carefully formulated products.

How Brands Use Citric Acid: Market Insight

In the beauty aisle, citric acid often appears in combination products rather than solo. It's commonly mixed with ingredients like salicylic acid for flaking or fungal concerns, lactic acid for gentle exfoliation, or nourishing oils. In a recent leave-in conditioner designed for scalp psoriasis, citric acid was used alongside salicylic acid and emollients to adjust pH and soothe the skin. That shows its versatility in tailored formulas—products aren’t selling citric acid alone, but touting it as part of a multi-actives strategy.

How You Encounter Citric Acid: Oral vs. Topical

While some people supplement citric acid orally (for example, in flavor enhancers or alkalinizing agents), its effects on scalp health are only meaningful when applied topically—via shampoos, conditioners, toners, or leave-ins. The mouse study mentioned earlier involved injections, which is far outside everyday use. In consumer hair care, its function is supportive—balancing pH, binding minerals, and reinforcing hair structure at the roots.

Bottom Line: Why It’s Really in the Bottle

Citric acid in scalp products is not just filler—it’s a scientifically supported ingredient that:

Balances pH, ensuring the scalp stays healthy and products are effective.
Chelates minerals, especially in hard water, to keep hair fresh.
Helps protect chemically treated hair, making it stronger and more resilient.
Integrates into multi-ingredient products, working alongside exfoliants or soothing agents.

When used in proper concentrations, citric acid is safe, widely accepted (it appears in official ingredient lists), and integral to modern cosmetology. It’s a subtle hero—not flashy, but it makes everything else perform better.

References

Zhang, D., Baghdadli, N., & Greaves, A. J. (2025, June). Reinforcing chemically treated human hair with citric acid. International Journal of Cosmetic Science, 47(3), 411–423. https://pubmed.ncbi.nlm.nih.gov/39757966
Xiangguang Shi et al. (2022, October). Disrupted citric acid metabolism inhibits hair growth. Journal of Dermatology, 49(10), 1037–1048. https://pubmed.ncbi.nlm.nih.gov/35841232/
Incidecoder. (n.d.). Citric Acid explained: buffering, chelating, etc. https://incidecoder.com/ingredients/citric-acid
Patel, S. A., Rout, S. P., Parmar, A. K., & Rajpurohit, K. S. (2025, March–April). Formulation and Evaluation of Leave-in Conditioner for Scalp Psoriasis. International Journal for Multidisciplinary Research, 7(2). [https://www.ijfmr.com/papers/2025/2/42686.pdf