The hydrophilic-lipophilic balance, or HLB, is a numerical scale that rates how water-loving or oil-loving a surfactant molecule is. Developed in the late 1940s by William Griffin, the scale typically runs from 0 to 20, where low numbers indicate a surfactant that prefers oil and high numbers indicate one that prefers water. It remains one of the most widely used tools in formulation science because it gives chemists a quick, practical way to pick the right surfactant for a given job, whether that job is stabilizing a moisturizing cream, delivering a drug through the gut, or helping a pesticide stick to a leaf.
What the Numbers Actually Mean
Think of every surfactant molecule as having a split personality. One end is hydrophilic, meaning it is attracted to water. The other end is lipophilic, meaning it is attracted to oils and fats. The HLB number captures which personality dominates. A surfactant with an HLB around 4 is strongly oil-loving and works well as a water-in-oil emulsifier, the kind used in heavy cold creams where a small amount of water is dispersed into a continuous oil phase. A surfactant with an HLB around 15 is strongly water-loving and is better suited for oil-in-water emulsions, the lighter lotions and milky serums where tiny oil droplets are suspended in water.
Rough functional ranges look like this:
- 1–3: Antifoaming agents
- 3–6: Water-in-oil emulsifiers
- 7–9: Wetting agents
- 8–15: Oil-in-water emulsifiers
- 13–15: Detergents
- 15–18: Solubilizers
These ranges overlap on purpose. The “right” HLB for a formulation depends not just on the surfactant but on the specific oil you are trying to emulsify. Every oil has what is called a required HLB, the surfactant HLB value at which the most stable emulsion forms. Mineral oil, for example, has a required HLB of about 10 for oil-in-water emulsions, while beeswax requires something closer to 9. When a formulator picks a surfactant whose HLB closely matches the oil’s required HLB, the emulsion tends to be more stable and more uniform in droplet size.
How HLB Values Are Calculated
Griffin’s original method was fairly straightforward for nonionic surfactants built from polyethylene oxide chains. For those molecules, the HLB is calculated directly from the weight percentage of the hydrophilic portion. A surfactant that is 80 percent hydrophilic by weight would have an HLB of about 16. The method works well for common nonionic surfactants used in cosmetics and food, but it does not handle ionic surfactants or more complex molecular architectures.
Davies later proposed a group contribution method that assigns a number to each chemical group in the molecule. Hydrophilic groups get positive values, lipophilic groups get negative values, and you add them all up with a baseline of 7. This approach expanded the system to cover ionic surfactants and more unusual structures. A refinement of this method using effective chain length instead of actual chain length improved accuracy, bringing the average error for over 200 nonionic surfactants down to less than 1.5 HLB units.1Elsevier / ScienceDirect (Journal of Colloid and Interface Science). Calculation of hydrophile–lipophile balance for polyethoxylated surfactants by group contribution method
Both approaches give you a single number for a surfactant, and that is their charm. A formulator can look up an HLB value in a table, compare it to the required HLB of an oil, and immediately know whether a surfactant is even in the right ballpark. In practice, though, most formulations use blends of two surfactants, one with a high HLB and one with a low HLB, mixed at ratios that produce an intermediate value matching the required HLB. This blending trick is the workhorse technique behind most emulsion development.
Measuring HLB Experimentally
Calculated HLB values are useful, but real-world surfactants are often complex mixtures of molecules rather than a single pure compound. Commercial surfactants sold under a brand name may contain dozens of related molecules with slightly different chain lengths, and a calculated HLB based on idealized structure can miss the mark. That is where experimental methods come in.
One well-established experimental approach uses the phase inversion temperature, or PIT. When you heat an oil-in-water emulsion stabilized by a nonionic surfactant, at a certain temperature the emulsion inverts and becomes water-in-oil. That crossover temperature is closely tied to HLB. Early work showed that for a given oil phase, the PIT increases in a roughly straight line as the surfactant HLB goes up.2Journal of Colloid and Interface Science. A DTA technique for identifying the phase inversion temperature of O/W emulsions By measuring the PIT and comparing it to a calibration curve, you can back out an HLB for surfactants that are hard to calculate from structure alone.
For commercial surfactants whose exact composition is unknown, the PIT method can be extended by mixing the test surfactant with a well-characterized reference surfactant and observing how the phase inversion shifts.3Journal of Colloid and Interface Science. Evaluation of the hydrophile-lipophile balance (HLB) of nonionic surfactants. II. Commercial-surfactant systems A newer refinement of this idea, called the PIT-deviation method, uses three calibration curves built from reference ethoxylated surfactants to rapidly assign HLB values to any amphiphilic ingredient.4PubMed. An efficient method to determine the Hydrophile-Lipophile Balance of surfactants using the phase inversion temperature deviation of C(i) E(j) /n-octane/water emulsions This kind of speed matters in industrial settings where a formulator may need to screen many surfactant candidates in a short time.
Cosmetic and Skincare Formulations
If you have ever noticed that some lotions feel light and watery while others feel rich and greasy, the HLB of the emulsifier system is a big part of the reason. Oil-in-water emulsions, which use high-HLB surfactants, feel lighter on the skin because water is the continuous phase that you sense first. Water-in-oil emulsions, made with low-HLB surfactants, feel heavier and more occlusive because oil is the phase surrounding everything.
A study on moisturizing creams and lotions demonstrated this by pairing glyceryl stearate (HLB of 3.8) with PEG-100 stearate (HLB of 18.8) at specific ratios to hit the required HLB of the oil phase. The researchers found that using the HLB method to guide development produced a more stable emulsion compared to a conventional trial-and-error approach.5Cosmetics. Investigation Utilizing the HLB Concept for the Development of Moisturizing Cream and Lotion: In-Vitro Characterization and Stability Evaluation For anyone formulating at home or in a small lab, this is practical guidance: rather than testing dozens of random surfactant blends, start by calculating the required HLB of your oil phase, pick a high-HLB and a low-HLB emulsifier, and blend them to hit that target. It will not guarantee a perfect product on the first try, but it dramatically narrows the search.
Beyond emulsion type, HLB also intersects with skin safety. Recent research evaluating surfactant-induced skin irritation found that how quickly surfactant molecules diffuse into the skin, along with their electrical charge and HLB, forms one of the main axes of variation in biological response.6PubMed. Mechanistic in vitro evaluation of surfactant-induced skin irritation: Correlating micellar physicochemistry with 3D reconstructed human epidermis, zein, and ecotoxicity endpoints In other words, HLB is not just about whether a cream stays mixed; it is also one piece of the puzzle determining how gentle or harsh a formulation feels.
Drug Delivery and Pharmaceutical Uses
Many promising drug molecules are poorly soluble in water, which means they are hard for the body to absorb when swallowed as a simple tablet. One way around this is to dissolve the drug in an oil and then create an emulsion that disperses easily in the gut. Self-emulsifying drug delivery systems, known as SEDDS, do exactly this. They are oily mixtures that spontaneously form fine emulsions when they contact the watery environment of the stomach and intestines.
For these systems, surfactant HLB is a critical design parameter. Surfactants with an HLB above 12 are typically chosen because they promote oil-in-water emulsification, creating tiny droplets that maximize the drug’s contact area with the gut lining and help it absorb faster.7PubMed Central. Self-emulsifying drug delivery systems: a novel approach to deliver drugs The specifics vary with the drug and oil used. Research on self-nanoemulsifying systems for the blood pressure medication nifedipine found that when using one family of surfactant blends, droplet size was essentially independent of HLB, but with a different surfactant family, higher HLB values produced smaller, nanosized droplets.8PubMed Central. Self-nanoemulsifying drug delivery system of nifedipine: impact of hydrophilic-lipophilic balance and molecular structure of mixed surfactants The takeaway is that HLB gives you a starting point, but the molecular architecture of the surfactant, not just its HLB number, shapes the final outcome.
The influence of specific molecular structure showed up clearly in a study that compared six surfactants all sharing an HLB of about 15 but differing in chain geometry and chemical features. Despite the identical HLB values, the surfactants produced nanoemulsions with meaningfully different stability profiles. The study found that a surfactant’s ability to lower the oil-water interfacial tension was the better predictor of long-term nanoemulsion stability, allowing formulators to anticipate shelf life.9Elsevier / Journal of Drug Delivery Science and Technology. Properties and stability of nanoemulsions: How relevant is the type of surfactant? HLB alone, in