Chlorhexidine: what it is, what it's for and which concentration to use

Chlorhexidine is in the mouthwash your dentist prescribes, in the antiseptic hospitals use before surgery, in surgical scrubs and in the teat dips that protect dairy cows. Few substances have had such a long career: it has been in use since the 1950s and is still the reference antiseptic in many protocols. Here we explain what it is, what it is used for, which concentration fits each job and how it differs from povidone-iodine and quats.

What is chlorhexidine?

Chlorhexidine is an antiseptic from the biguanide family. The British company Imperial Chemical Industries (ICI) developed it in the early 1950s while looking for antimalarial drugs, and it has been used in medicine, dentistry and veterinary care ever since.

The base molecule barely dissolves in water, so it is almost always used as a salt. The most common one is chlorhexidine gluconate (also called chlorhexidine digluconate, CAS 18472-51-0), sold as a 20% aqueous solution. That concentrate is the raw material for mouthwashes, antiseptics and soaps: nobody applies it as is.

How does it work?

Chlorhexidine carries a positive charge and bacterial cell walls carry a negative one. So it sticks to the cell, disrupts its membrane and makes it leak its contents. At low concentrations it stops bacteria from growing; at high concentrations it kills them.

Its big advantage is substantivity: it binds to skin and mucous membranes and is released slowly, so it keeps working for hours after application. Alcohol acts faster but evaporates and leaves no residual effect. That is why many antiseptics combine the two.

It is very effective against gram-positive bacteria, good against gram-negatives and yeasts, and acts on enveloped viruses. It does little against non-enveloped viruses and mycobacteria, and it does not kill spores.

What chlorhexidine is used for, by concentration

The same molecule does very different jobs depending on how far it is diluted:

It is also used as a preservative in cosmetics. In the European Union the limit is 0.3% expressed as chlorhexidine.

How to dilute 20% chlorhexidine gluconate

To make a solution from the concentrate, use C₁ × V₁ = C₂ × V₂. For one liter of finished product:

• 4%: 200 mL of concentrate, made up to 1 L.
• 2%: 100 mL of concentrate.
• 0.5%: 25 mL of concentrate.
• 0.2%: 10 mL of concentrate.
• 0.12%: 6 mL of concentrate.

Dilute with purified or deionized water: chlorides, sulfates and carbonates in tap water can make chlorhexidine precipitate. And before launching a product, validate the formula in the lab and check which registration it needs with COFEPRIS or, for veterinary use, SENASICA (we explain it in SAGARPA/SENASICA registration for disinfectants).

Chlorhexidine mouthwash: what to know

0.12% chlorhexidine mouthwash is one of the most prescribed in dentistry to control plaque and gum inflammation, for example after dental surgery. Three things worth knowing:

• It is meant for short courses. With prolonged use it can stain teeth brown and change how food tastes. The stains are not permanent and come off with a dental cleaning.
• It doesn't mix well with toothpaste. The sodium lauryl sulfate in many toothpastes inactivates it, so leave some time between brushing and rinsing.
• Always follow your dentist's instructions on dose and length of treatment.

Chlorhexidine vs. povidone-iodine vs. quats vs. alcohol

In surgery, chlorhexidine combined with alcohol has shown fewer surgical-site infections than povidone-iodine in clinical studies, which is why many hospital guidelines prefer it for skin preparation. Povidone-iodine remains the alternative when there is a chlorhexidine allergy and on mucous membranes. To learn more about iodine, read iodine in industry: uses you didn't know about.

Compatibility and handling in the plant

• Surfactants: it is compatible with nonionic and cationic surfactants. Anionics such as sodium lauryl sulfate inactivate it.
• pH: it works best between 5 and 8. Above pH 8 the free base can precipitate.
• Chlorine: fabric treated with chlorhexidine and then washed with hypochlorite can be left with brown stains. Hospital laundries use chlorine-free bleaches.
• Storage: in a closed container, protected from light and away from heat. Prolonged heating degrades it.
• Safety: avoid contact with the eyes and the middle ear. Although rare, it can cause allergic reactions. Always check the safety data sheet.

Frequently asked questions

What is chlorhexidine used for? To reduce bacteria on skin, in the mouth and on hands, and to protect the udders of dairy cattle. It is used in mouthwashes, surgical antiseptics, hand soaps and teat dips.

Which is better, chlorhexidine or povidone-iodine? It depends on the use. Chlorhexidine leaves a residual effect and, combined with alcohol, is preferred for skin preparation before surgery. Povidone-iodine has a broader spectrum and is the alternative when there is a chlorhexidine allergy.

Are chlorhexidine gluconate and digluconate the same? Yes. They are two names for the same salt, the water-soluble form of chlorhexidine.

Why does chlorhexidine stain teeth? It sticks to the tooth surface and traps pigments from coffee, tea or wine. The stains come off with a professional dental cleaning.

Can chlorhexidine be mixed with soap? Not with regular soap or anionic surfactants: they inactivate it. Chlorhexidine surgical scrubs are formulated with nonionic surfactants.

Where can I buy chlorhexidine gluconate in Mexico? At Quimiconsult, from Monterrey, with shipping across Mexico and a certificate of analysis for every lot.

How Quimiconsult helps

At Quimiconsult we distribute chlorhexidine and other antiseptics from Monterrey, Nuevo León, with shipping across Mexico:

• Chlorhexidine gluconate 20% USP grade: 19 to 21% active content by HPLC, in 20 L jerrycans, 50 and 200 L drums and 1000 L totes.
• Dioxel antibacterial solution: ready-to-use hand antiseptic with 0.5% chlorhexidine and 70% alcohol.
• Povidone-iodine USP: for when you need the iodine-based alternative.
• Benzalkonium chloride 50%: a quat for surface disinfection and preserving formulas.
• Documentation and support: certificate of analysis per lot, technical data sheet, safety data sheet and formulation advice.

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