HLB System Explained: A Practical Guide to Stable Emulsions

Why Your Emulsions Keep Separating

You followed the recipe exactly. You heated your phases to the right temperature. You blended at high speed. And three days later, your lotion has a layer of oil floating on top.

This is the most common frustration in cosmetic formulation, and the answer almost always traces back to one concept: HLB, or the Hydrophilic-Lipophilic Balance system. Understanding HLB is the difference between emulsions that hold together for months and products that separate on the shelf before they ever reach a customer.

This guide will give you a practical, working understanding of HLB. Not the deep chemistry, but the hands-on knowledge you need to formulate stable creams, lotions, and other emulsions with confidence.

What HLB Actually Means

Every emulsifier has a dual personality. One part of its molecular structure is attracted to water (hydrophilic). The other part is attracted to oil (lipophilic). The HLB value is a number on a scale of 0 to 20 that describes which tendency dominates.

• Low HLB (0-9): More oil-loving. These emulsifiers are better at stabilizing water-in-oil (W/O) emulsions, like cold creams and heavy balms.
• High HLB (10-20): More water-loving. These emulsifiers are better at stabilizing oil-in-water (O/W) emulsions, like lotions and lightweight creams.

Think of the HLB value as a personality score. A low number means the emulsifier prefers to hang out with oils. A high number means it prefers water. Your job as a formulator is to match the emulsifier's personality to the needs of your specific oil blend.

Why HLB Matters for Stability

Oil and water do not mix on their own. An emulsifier sits at the boundary between oil droplets and the water phase, preventing the droplets from merging back together. But here is the critical point: different oils require different amounts of stabilization effort, and not every emulsifier is equally suited to every oil.

Each oil has a required HLB value, which is the HLB number an emulsifier needs to have in order to keep that particular oil dispersed in water (for O/W emulsions). If your emulsifier system's HLB does not match what your oil blend requires, the emulsion will be inherently unstable. It might look fine at first but will eventually separate.

Matching your emulsifier system to your oil phase's required HLB is the foundation of stable formulation.

Required HLB Values for Common Oils and Butters

Every oil and butter used in cosmetics has been assigned a required HLB value through testing. Here are the values for ingredients you are most likely to encounter.

Carrier Oils

Oil	Required HLB
Sweet almond oil	7
Jojoba oil	6
Coconut oil (fractionated)	8
Grapeseed oil	7
Avocado oil	7
Argan oil	7
Castor oil	14
Mineral oil	10-12
Sunflower oil	7
Hemp seed oil	7

Butters and Waxes

Ingredient	Required HLB
Shea butter	8
Cocoa butter	6
Mango butter	8
Beeswax	9
Lanolin	10
Cetyl alcohol (fatty alcohol)	13
Stearic acid	15

Other Common Ingredients

Ingredient	Required HLB
Isopropyl myristate	11.5
Cetyl esters	10
Caprylic/capric triglyceride (MCT)	5
Dimethicone (low viscosity)	7-8
Squalane	8

Note that these values are for oil-in-water emulsions. If you are making a water-in-oil emulsion, the required HLB shifts lower, and a different set of reference tables applies.

Common Emulsifiers and Their HLB Values

Now that you know what your oils need, here are the HLB values of emulsifiers commonly used in cosmetic formulation.

High HLB Emulsifiers (Water-Loving)

Emulsifier	HLB Value
Polysorbate 80 (Tween 80)	15.0
Polysorbate 20 (Tween 20)	16.7
PEG-100 stearate	18.8
Ceteareth-20	15.7
BTMS-50 (Behentrimonium methosulfate blend)	~15
Steareth-20	15.3

Low HLB Emulsifiers (Oil-Loving)

Emulsifier	HLB Value
Sorbitan stearate (Span 60)	4.7
Sorbitan oleate (Span 80)	4.3
Glyceryl monostearate (GMS)	3.8
Cetearyl alcohol	3.5
Sorbitan palmitate (Span 40)	6.7
Steareth-2	4.9

Complete Emulsifying Systems

Some ingredients are sold as pre-blended emulsifying systems with a target HLB already built in. These simplify formulation considerably.

System	Effective HLB	Best For
Emulsifying wax NF	~12	General O/W lotions
Olivem 1000	~10	Natural O/W creams
BTMS-25	~11	Conditioning emulsions
Montanov 68	~11	Eco-cert O/W formulas

If you are just starting out, a pre-blended system is perfectly fine. As your skills grow, blending your own emulsifiers gives you more control.

How to Calculate Required HLB for a Multi-Oil Blend

Most formulas contain more than one oil. To find the required HLB for your complete oil phase, you calculate a weighted average based on the proportion of each oil.

The formula is:

Required HLB = (% Oil A x HLB of A) + (% Oil B x HLB of B) + ... / Total Oil Phase %

Or more simply: multiply each oil's percentage of the total oil phase by its required HLB, then add them all up.

Example Calculation

Say your oil phase is:

Oil	Amount	% of Oil Phase	Required HLB
Sweet almond oil	10g	40%	7
Shea butter	8g	32%	8
Coconut oil	5g	20%	8
Beeswax	2g	8%	9
Total	25g	100%

Required HLB = (0.40 x 7) + (0.32 x 8) + (0.20 x 8) + (0.08 x 9)

Required HLB = 2.80 + 2.56 + 1.60 + 0.72

Required HLB = 7.68

Your emulsifier system needs to have an HLB of approximately 7.7 to optimally stabilize this oil blend.

How to Blend Two Emulsifiers to Hit Your Target HLB

Here is where HLB becomes genuinely powerful. By blending a high-HLB emulsifier with a low-HLB emulsifier, you can dial in to any target HLB value with precision.

The formula to find the ratio is:

% Emulsifier A = (Target HLB - HLB of B) / (HLB of A - HLB of B) x 100

% Emulsifier B = 100 - % Emulsifier A

Example: Hitting HLB 7.7

You want to reach an HLB of 7.7 using Polysorbate 80 (HLB 15) and Span 60 (HLB 4.7).

% Polysorbate 80 = (7.7 - 4.7) / (15.0 - 4.7) x 100

% Polysorbate 80 = 3.0 / 10.3 x 100

% Polysorbate 80 = 29.1%

% Span 60 = 70.9%

If your total emulsifier amount is 5g (a typical amount for a 100g batch), you would use:

• Polysorbate 80: 5g x 0.291 = 1.46g
• Span 60: 5g x 0.709 = 3.54g

This blend will produce an emulsifier system with an effective HLB of 7.7, which matches what our example oil phase requires.

Oil-in-Water vs. Water-in-Oil Emulsions

The type of emulsion you are making determines which side of the HLB scale you work with.

Oil-in-Water (O/W)

This is the most common type in cosmetics. Oil droplets are dispersed in a continuous water phase. The result feels light, absorbs quickly, and is non-greasy. Lotions, lightweight creams, and most moisturizers are O/W emulsions.

O/W emulsions require emulsifiers with HLB values of 8-16, depending on the oil phase. The water phase is typically 60-80 percent of the formula.

Water-in-Oil (W/O)

Water droplets are dispersed in a continuous oil phase. The result feels rich, occlusive, and protective. Cold creams, night creams, and some sunscreens are W/O emulsions.

W/O emulsions require emulsifiers with HLB values of 3-8. The oil phase is a larger proportion of the formula, often 40-60 percent.

How to Tell Which Type You Have

A simple test: drop a small amount of your finished emulsion into a glass of water. If it disperses easily, it is O/W. If it sits on the surface or sinks as a blob, it is W/O.

The type of emulsion is primarily determined by the HLB of your emulsifier system, the phase ratio, and the order of addition during processing.

Troubleshooting Common Emulsion Problems

Even with correct HLB calculations, emulsions can fail. Here are the most common issues and their likely causes.

Separation (Oil Layer on Top)

• HLB mismatch: Your emulsifier system's HLB does not match your oil phase requirements. Recalculate.
• Insufficient emulsifier: Most O/W emulsions need 3-6 percent total emulsifier. If you are below 3 percent, increase it.
• Temperature shock: Cooling too quickly can destabilize an emulsion. Cool gradually while stirring.
• Contamination: Water introduced during use (wet fingers in jars) promotes microbial growth, which can break emulsions.

Graininess or Beadiness

• Crystallization of fatty alcohols or waxes: Your oil phase cooled too quickly, forming crystals instead of integrating smoothly. Heat both phases to at least 70-75C and combine at the same temperature.
• Incomplete melting: All solid ingredients must be fully melted before combining phases.
• Overuse of stearic acid or cetyl alcohol: These can crystallize at high concentrations. Keep stearic acid below 5 percent and cetyl alcohol below 4 percent unless your formula specifically accounts for it.

Thinning Over Time

• Preservative failure: Microbial contamination breaks down emulsifiers. Ensure your preservative system is effective and properly dosed.
• Phase inversion: The emulsion has flipped from O/W to W/O or vice versa due to temperature changes or mechanical stress.
• Evaporation: If the product is not in an airtight container, water loss changes the phase ratio.

Instability After Adding Fragrance or Actives

• Fragrance oils can destabilize emulsions, especially if they contain solvents or high amounts of certain terpenes. Add fragrance below 40C and at the minimum effective percentage.
• Some actives change pH, which can affect emulsifier performance. Check pH after adding actives and adjust if needed.

When HLB Is Not Enough

The HLB system is a powerful starting point, but it has real limitations. It was developed in the 1950s for a narrower range of ingredients than what modern formulators use. There are situations where hitting the right HLB number alone will not save your emulsion.

Co-Emulsifiers

A single emulsifier, even at the right HLB, often produces less stable emulsions than a blend of two or more emulsifiers. This is why the dual-emulsifier approach described above is not just a calculation convenience. It produces genuinely better results. The two emulsifiers pack more efficiently at the oil-water interface than either one alone.

Thickeners and Stabilizers

Thickeners like xanthan gum (0.2-0.5%), hydroxyethylcellulose, or carbomer increase the viscosity of the water phase, which slows down the movement of oil droplets and reduces the chance of coalescence. Many professional formulations include a thickener as a stability insurance policy, even when the emulsifier system is strong.

Co-stabilizers like cetyl alcohol and stearic acid reinforce the emulsifier film at the oil-water interface. They are not emulsifiers on their own, but they dramatically improve the performance of your primary emulsifiers.

Processing Matters

Even a perfectly calculated HLB will fail if your processing technique is wrong. Key process variables include:

1. Temperature: Both phases should be heated to 70-75C before combining
2. Addition order: Generally, add the oil phase to the water phase for O/W emulsions
3. Mixing speed: High-shear mixing creates smaller, more uniform oil droplets
4. Cooling rate: Slow, controlled cooling with continuous stirring produces the most stable results
5. Homogenization: A stick blender or homogenizer significantly improves particle size uniformity

Modern Emulsifying Systems

Many newer emulsifiers, particularly those based on polyglycerol esters, alkyl polyglucosides, and self-emulsifying systems, do not fit neatly into the traditional HLB framework. They work through different mechanisms, such as liquid crystal formation, and are better evaluated through direct stability testing rather than HLB calculations.

If you are using ingredients like Olivem 1000, Montanov 68, or Simulgreen 18-2, follow the manufacturer's usage guidelines rather than trying to calculate HLB values.

Putting It All Together

The HLB system gives you a rational starting point for formulating stable emulsions. Instead of guessing which emulsifier to use and hoping for the best, you can:

1. List your oil phase ingredients and their required HLB values
2. Calculate the weighted average required HLB for your blend
3. Select two emulsifiers (one high HLB, one low HLB) and calculate the ratio needed to hit your target
4. Formulate your batch with proper technique: matching temperatures, correct addition order, and adequate mixing
5. Test stability over 4-8 weeks at room temperature and under stress conditions (heat, cold, freeze-thaw cycles)

If the emulsion fails, adjust the HLB up or down by 0.5-1.0 and test again. Most oil blends have a stability window of plus or minus 1 HLB unit from the calculated optimum.

Formuley's built-in HLB calculator handles the math for you. Enter your oil phase ingredients and their percentages, and it returns the required HLB along with suggested emulsifier blends from your inventory. It takes the calculation out of your notebook and puts it where it belongs: integrated with your formula records so you can track what worked, what did not, and why.

Stable emulsions are not magic. They are math, technique, and patience. The HLB system gives you the math. Practice gives you the technique. And methodical record-keeping gives you the pattern recognition to get it right faster every time.