There are likely between eight and fifteen products sitting on your bathroom shelf right now. They all look different, feel different, and work differently — but few people stop to think that behind this variety lies a strict classification. Not a marketing one, but a chemical one. The form of the formula determines everything: stability, the efficiency of active delivery, the skin feel, and even how long the product will last on your shelf. If you have ever tried to formulate something of your own and felt like you were starting from the wrong end, this is most likely where the problem was.
Why the form of the formula is more important than the ingredient list
A cosmetic chemist thinks about a product differently than a consumer. While a buyer reads "hyaluronic acid" and "niacinamide," a chemist sees a system: a dispersed phase, a continuous phase, a rheological profile, and thermodynamic stability. It is the system that decides whether the active substance will get where it needs to go or just be washed down the drain.
Let's take a simple example: vitamin C. In an aqueous solution at pH 3.5, it works differently than in an anhydrous oil stick or an emulsion at pH 5.5. The molecule is the same, but the system is different, and the result is different. That is why understanding formula types is not academic boredom, but a practical tool.
Ten basic categories that cover almost everything
The classic classification of cosmetic formulas looks like this:
- Solutions
- Creams and emulsions
- Lotions
- Ointments and pastes
- Suspensions
- Tablets and pressed forms
- Powders
- Gels
- Sticks
- Aerosols
Each of them is a separate chemical universe with its own laws, problems, and beauty. Let's go through the key ones.
Solutions: deceptive simplicity
Toners, micellar water, floral waters, perfumes, and most shampoos — these are all solutions. They are homogeneous mixtures where all ingredients are dissolved in a single solvent (most often water, sometimes ethanol or a mixture). No phases, no phase boundaries. They are thermodynamically stable — and that is their main advantage.
But the "simplicity" here is deceptive. Try to introduce a fat-soluble active into an aqueous solution, and the system will instantly turn into a suspension or an emulsion. Or it won't turn into anything and will simply precipitate. Solubility is not a given; it is a parameter that must be managed: through pH, through temperature, and through co-solvents like Propylene Glycol or Butylene Glycol.
When a solution becomes a problem
The main pain point of aqueous solutions is microbiological instability. Water is an ideal environment for the growth of bacteria and mold. If you formulate a toner without a proper preservation system, in two weeks it is no longer cosmetics. Standard practice is a combination of preservatives with overlapping spectra of activity: for example, Phenoxyethanol (up to 1%) paired with Ethylhexylglycerin (0.3–0.5%). Read more about how pH affects the effectiveness of preservatives in our article pH in cosmetics: a basic guide for formulators.
Emulsions and creams: the most complex and most popular form
If solutions are a monologue, then emulsions are a dialogue between two incompatible elements. Water and oil do not want to mix — this is a thermodynamic fact. An emulsifier acts as a mediator, reducing interfacial tension and allowing one liquid to disperse into the other in the form of tiny droplets.
The size of these droplets — from 0.1 to 100 µm — determines the texture, appearance, and stability of the product. The smaller the droplets, the more stable the emulsion and the more "silky" the cream feels on the skin. Nanoemulsions with droplets smaller than 200 nm look transparent — this is why some "light fluids" are not white, but almost transparent.
O/W vs W/O: not just abbreviations
An "oil-in-water" (O/W) emulsion is the most common type. The water phase is continuous, the oil phase is dispersed. The result is a light texture, fast absorption, and a feeling of freshness. Most day creams, lotions, and BB creams are O/W.
A "water-in-oil" (W/O) emulsion is the opposite story. The oil phase is continuous, the water phase is dispersed. It has a richer texture, an occlusive effect, and better protection against transepidermal water loss (TEWL). Night creams, some sunscreens, and cold creams are often W/O. Paradoxically, W/O creams can moisturize the skin more effectively precisely because they create a barrier.
Choosing the type of emulsion is a strategic decision made before you even open your ingredient spreadsheet. If you are just starting your journey in formulation, take a look at our article How to become a cosmetologist: the path from curiosity to professional formulation — it contains important context on where to begin.
Lotions: emulsions with character
Technically, a lotion is the same O/W emulsion, but with a higher water content (usually 70–85%) and a smaller amount of the oil phase (5–15%). This makes them more fluid, less rich, and ideal for large areas of the skin — the body, legs, and arms. Rheologically, they differ from creams: the viscosity of a lotion is usually 3,000–8,000 mPa·s, compared to 30,000–80,000 mPa·s for a thick cream.
Gels: water with character
A gel is a structured liquid. A polymer network (gelling agent) holds the water, creating a system with high viscosity at rest and fluidity under mechanical stress — what rheologists call thixotropy. Carbomer (Carbopol), Hydroxyethylcellulose, Xanthan Gum — each creates a gel with a unique profile: different gloss, different "stringiness," and a different feel on the skin.
Gels are especially popular in oily skin care: they do not add oils, they cool, and they provide a feeling of cleanliness. But they have an Achilles' heel — hydrophobic actives do not dissolve in them. Want to incorporate shea butter or retinol into a gel? You will either have to solubilize them or switch to a different form. How gums and gelling agents affect the texture and functionality of a product is described in detail in our article Tribology, gums, and gelling agents.
Ointments, pastes, and anhydrous formulas: when water is the enemy
There is an entire class of products where water is fundamentally absent. Ointments are, as a rule, mixtures of waxes, oils, and fatty alcohols without an aqueous phase. Petrolatum is the archetype. Pastes are the same, but with the addition of powdered components (kaolin, zinc oxide, starch) at 50% or higher.
Anhydrous systems are thermodynamically stable — bacteria do not grow in them, and they do not need preservatives in the classic sense. They create a powerful occlusive barrier, reducing TEWL to a minimum. But the sensation on the skin is a different story: most people find thick ointments "greasy" and uncomfortable. This is precisely why cosmetic chemistry over the last twenty years has been actively working on lightening textures without losing functionality. If you are interested in the topic of anhydrous systems, we have a detailed article: Anhydrous products: A complete guide for beginners.
Sticks: an anhydrous form with geometry
A stick is, in essence, an anhydrous formula that has been shaped using structuring waxes. Lip balm, deodorant sticks, solid perfumes, highlighters — these all follow the same philosophy: melt, pour into a mold, and cool. The key parameter is the melting point of the final mixture. If it's too low, the stick will "melt" in your pocket during the summer. If it's too high, it will be difficult to apply. The optimal range is 55–65°C for most applications.
The wax profile determines everything: Carnauba Wax provides shine and hardness, Candelilla Wax is a vegan alternative to beeswax with similar properties, and Microcrystalline Wax provides plasticity and adhesion. By combining them in different proportions, you can achieve a texture ranging from a "creamy lipstick" to a "hard pencil."
Suspensions, powders, and aerosols: special formats
Suspensions: when particles don't want to dissolve
A suspension is a system where solid, insoluble particles are dispersed in a liquid. A classic example is a mineral sunscreen with Titanium Dioxide or Zinc Oxide. The particles physically scatter UV radiation, but they are prone to agglomeration and sedimentation. This is exactly why the bottle says "shake before use."
Stabilizing suspensions is an art in itself. This is where thickeners come in, creating a structured network that keeps the particles in suspension. Xanthan Gum at a concentration of 0.3–0.5% creates what is known as "yield stress"—a threshold below which the system behaves like a solid and the particles do not settle. A comparison of xanthan and guar for such tasks can be found in our article Xanthan and guar gums: comparison, synergy, and an unexpected winner.
Powders and pressed forms
Powders, eyeshadows, blushes, and loose mineral products are systems made of a mixture of powders with different functions: fillers (talc, mica, kaolin), pigments (iron oxides, ultramarine), and binders (oils, waxes in small quantities). Pressed forms add binding agents and pressure ranging from 50 to 200 kg/cm² to this process.
Powder rheology is a science of its own: flowability, angle of repose, and bulk density. All of these factors influence how the product is applied, how it sits on the skin, and how long it lasts.
Aerosols: pressure as a tool
An aerosol format is any of the aforementioned formulas plus a propellant under pressure. Hairspray, deodorant spray, heat protectant spray, sunscreen aerosol. The propellant (most often mixtures of butane, propane, isobutane, or compressed nitrogen for "natural" options) evaporates upon exiting the valve, spraying the formula as a fine mist.
From a regulatory standpoint, aerosols are the most complex category: pressure, flammability, specialized packaging, and VOC (volatile organic compound) restrictions in different jurisdictions.
A special case: soap and the saponification process
Soap stands apart in this classification — it is not just a "cleansing product," it is the result of a chemical reaction. Saponification — the reaction between fatty acids (found in oils and fats) and an alkali (sodium hydroxide for solid soap, potassium hydroxide for liquid) — creates an entirely new substance: a fatty acid salt, which is what soap actually is.
This fundamentally distinguishes soap from synthetic detergents (syndets): the latter are surfactants obtained through chemical synthesis, without a saponification reaction. The pH of real soap is 9–10, which is both its advantage (the alkaline environment effectively destroys bacterial membranes) and its weakness (irritation for sensitive skin with a compromised barrier). You can find detailed information on the chemistry of soap making, calculating saponification values, and choosing oils in our extensive article: Handmade soap: chemistry, formulation, and everything you need to know before buying or making it.
Every oil in a soap formula makes its own contribution: coconut oil (Cocos Nucifera Oil) provides lather and hardness, olive oil (Olea Europaea Fruit Oil) provides softness and a conditioning effect, and castor oil (Ricinus Communis Seed Oil) provides foam stability. And the composition of these oils, by the way, varies depending on the climate in which they are grown — we have a separate analysis on this: How climate affects the fatty acid and essential oil composition in plants.
How to choose the right form for your idea
When you have a product idea, the first question is not "what actives do I want to use," but "which form will best deliver them to where they are needed." Here is a simplified checklist:
- Water-soluble actives + light hydration → solution or light O/W gel
- Combination of water- and oil-soluble actives → O/W or W/O emulsion
- Maximum barrier effect, sensitive skin → ointment or W/O emulsion
- Oily skin, light hydration without oils → gel based on Carbomer or Hydroxyethylcellulose
- Cleansing with foam formation → surfactant-based solution or soap (taking pH into account)
- Convenient application to lips/body without pump packaging → stick
- Mineral UV filter → suspension in an emulsion or gel
- Long-lasting makeup → pressed powder or anhydrous emulsion
These are not rigid rules — cosmetic chemistry is full of hybrid solutions. A gel-cream is an O/W emulsion with a gel-like texture. A cushion is a suspension of pigments in an emulsion, soaked into a sponge. A transformer oil is an anhydrous formula that emulsifies upon contact with water on the skin. Understanding the basic types is the foundation upon which all these innovations are built.
How does an emulsion differ from a lotion — are they completely different things?
A lotion is a subtype of an O/W emulsion with a high water content (70–85%) and low viscosity. All lotions are emulsions, but not all emulsions are lotions. A cream is also an O/W or W/O emulsion, but with a higher content of the oil phase and thickeners, which provides a denser texture and higher viscosity. The line between "lotion" and "cream" is blurred in marketing, but chemically, the difference in the rheological profile and phase ratio is quite specific.
Why can't soap be considered a regular cosmetic solution?
Soap is the product of a chemical saponification reaction, not just the mixing of ingredients. Unlike solutions, where components retain their chemical identity, in the saponification process, fats and alkali react to form a new substance — a fatty acid salt. This fundamentally changes the product's properties: pH 9–10, a specific cleansing mechanism via micelle formation, and sensitivity to hard water (formation of "soap scum"). This is precisely why soap is regulated differently than synthetic detergents in many jurisdictions.
Can essential oils be added to an aqueous solution without an emulsifier?
No, without a solubilizer, essential oils will not dissolve in water — they will simply float on the surface or form a cloudy suspension. For clear solutions (toners, sprays), you need a solubilizer — for example, Polysorbate 20 or Caprylyl/Capryl Glucoside in a concentration sufficient to fully solubilize the oil. The standard ratio is 3–5 parts solubilizer to 1 part essential oil, but this varies depending on the specific oil and system.
Understanding formula types is not just theory for an exam. It is the language that cosmetic chemistry speaks. When you see a product on a shelf, you start to read it differently: not as a list of ingredients, but as a system with logic. And it is precisely this logic that allows you to create something that works, rather than just something that smells nice. If you want to learn how to formulate consciously — with an understanding of the chemistry behind every decision — we have a course: check out the Formula cream Club.
