From creams to tonics - an overview on different types ...

Haptic-, sensorial properties and practicability of products often are the decisive factors for consumers. The actual aim, however, is effectiveness which depends on how the components are processed - in other words, in an aqueous solution, a gel or in an emulsion. The different types of application are crucial for certain properties, as for instance how fast and how long the formulation is effective. They also influence the grade of availability of active agents in the skin.

Additional criterion to consider: the specific cosmetic additives in the different types of application that can have synergistic effects but also negatively influence the skin care- and environmental properties. Just to mention some examples: penetration-enhancing substances increase the availability of substances; preservatives affect the microbiome of the skin; perfumes have allergenic potential; other cosmetic additives are physiologically or biologically not degradable. Cosmetic additives can also be highly effective active agents - such as native phosphatidylcholine in liposomes and nanodispersions or hydrogenated phosphatidylcholine in lamellar creams.

The pH value is a significant criterion in all aqueous applications. Without buffers it can range from 5-7. In cases where salt components buffer the pH value, or in other words, keep it at a constant level, the pH level should match the individual pH value of the skin. Should that not be the case, there is a risk of disorders in the skin barrier, of the epidermal enzymes and of the microbiome.

Combinations of the different types of application with instrument-based treatments such as the iontophoresis (aqueous solutions with mostly negatively charged active agents), radiofrequency (RF; high energy input), ultrasound, medical needling (dermal needling) should only be carried out by staff who is qualified for instrument-based treatments and has a certain knowledge on the suitability of the preparations and their contents. Examples:

The table below gives an overview on different applications in the sections skin cleansing, skin protection, skin care and decorative cosmetics.

Type of application

Composition

Additives

Typical usage

Hints

Solutions - aqueous

Water-soluble herbal extracts, vitamins, amino acids, moisturizing substances (glycerin, urea etc.), hyaluronic acid in low concentration

Preservatives¹, alternatively: cans and ampoules (sterile) or low alcohol- and glycol-contents

Sera (possibly modular), moisturizers, tonics, lotions, antimicrobial dermal needling tonics

Filling possibly in aerosol cans with propellant gas, dispensers with spraying- or foaming attachment² or pipette bottles

Water, tensides

Tensides⁸ in low concentration; preservatives¹

Micelle water, mild skin cleansing

Rinse-off-products

Solutions - alcoholic

Essential oils, perfumes

High alcohol- or isopropyl alcohol contents

Fitness frictions (cooling), inunctions, perfumes

Not suitable for skin care purposes

Solutions - non-aqueous

Organic, liquid solvents

None

Nail enamels

Not suitable for skin care purposes

Essential oils

Volatile herbal extracts, e.g. rose oil (alias attar)

None

Perfumes, bath- and cream additives, room scents, aromatherapy

Follow Dangerous Substances Directive

Fatty oils

Native triglycerides and/or synthetic ester oils

Antioxidants³ at triglycerides with bound essential fatty acids

Massage oils, body oils, baby cleansing and baby skin care

Suitable for atopic, very dry and sensitive skin

Butters

Shea- and cocoa butter contain cholesterol-like phytosterines and wax esters

None

Lipid-rich skin care, frequently locally applied, e.g. breast and genital area

Suitable for atopic, very dry skin, very economical product, slow penetration

Balms - e.g. benzoin, frankincense, myrrh

Natural herbal secretions containing essential oils, free acids, aromatic esters and aldehydes

Balms and their extracts lose their resin characteristics when processed in nanodispersions

Anti-inflammatory sera

Suitable for rosacea and acne skin care: boswellic acids (frankincense extract)

Hydrogels

Water and gelling agents, e.g. xanthan gum, hyaluronic acid or synthetic carbomers

Preservation see aqueous solutions

Hair- and skin care, modular base gels, moisturizers, cleansing gels (with tensides)

Ultrasound medium

Oleogels - degradable

Triglycerides, wax esters, phytosterines

Penetration-enhancing substances: phosphatidylcholine⁴

Child care, skin protection, in particular cases suitable for rosacea skin care

Good penetration; suitable for atopic and very dry skin

Oleogels - mineral

Paraffin oils, vaseline, ceresin waxes, (ozokerite)

Frequent consistency agent: silica

Ointments, topical pharmaceutical drugs, mascara, camouflages and eye shadows

Poor penetration (occlusive), regenerative processes are slowed down (plaster effect)

Sticks

Waxes, pigments, fatty oils

Antioxidants

Lip(care)sticks, eyeliner pencils and concealer sticks

Semisolid to solid

Shake mixtures

Oil and water

Emulsifier free, preservation see aqueous solutions

Sensitive skin, problem skin, pharmaceutical drugs

Shake well before use

Emulsions⁵

Oil in water (O/W)

O/W-emulsifiers⁶, preservatives¹, preservative free: foams (aerosol cans), aqueous phase frequently hypertonic⁷

Mild skin care (creams, milk) tenside free cleansing (milk)

Reduced washout effect in case of physiologically compatible emulsifiers: e.g. mono- and diglycerides

Water in oil (W/O)

W/O emulsifiers⁶,

preservatives¹

Rich skin care, skin protection

In comparison to O/W mostly lower water phase and less preservatives¹

Pickering emulsions

Solids such as silica, peptides (in the interfaces)

Skin care

W/O and O/W possible

Cold creams

Lanolin, phytosterines, bees wax, low amounts of water

Salts

Dry and sensitive skin

In comparison to W/O emulsions a more solid consistency

Lamellar bases

Oils and water in the form of physiological membrane structures

Phosphatidylcholine⁴

Skin protection, skin care, modular base creams: emulsifier free cleansing (milk)

Particularly suitable for dry and atopic skin; suitable for corneotherapeutic treatments (according to A.M.Kligman)

Microemulsions

Water, tensides, oil

Tensides⁸ in high concentration

Transparent shampoos, cleansing gels

High skin irritation potential in tensides with high critical micelle concentration (CMC), rinse-off products

Nanodispersions

Water, particles with physiological membranes and encapsulated liquid, lipophilic active agents

Phosphatidylcholine⁴

Active agent concentrates, sera (possibly modular) - frequently for problem skin. Specific bath preparations (in-situ dispersions)

High penetration of active agents; particularly suited for dry and atopic skin as well as scars; particles physiologically degradable

Water, solid lipophilic active agent particles in nano size

Tensides⁸

Active agent concentrates, sera, compound for skin care preparations

High penetration of not readily soluble active agents; particles physiologically degradable

Liposomes

Water, cellular physiological bilayer with encapsulated hydrophilic active agents

Phosphatidylcholine⁴

Active agent concentrates, sera (possibly modular) - frequently for problem skin

High penetration of active agents, particularly suitable for blemished skin, acne, perioral dermatitis

Suspensions

Micronized active agents

Cream bases

Ointments, UV-protection (mineral: ZnO, TiO₂)

Not readily soluble active agents

Waxes, seed flours

Cream bases

Mechanical peelings plus skin care ("2 in 1")

Waxes are more gentle to the skin than seed flours

Plastic particles consisting of PE, PP, PU

Cream bases

Mechanical peelings, occupational skin cleansing

Microplastics problems

Salts or sugars, fatty oils or oil mixtures

Mixture to prepare before the treatment

Full-body peelings plus skin care ("2 in 1")

Peeling bodies are removed with water after the treatment

Pigments, dyes, polyamide fibres

Mascara base

Mascara

Eye cosmetics (deco)

Foundations

Emulsions with high pigment content

Emulsifiers⁶, emulsifier free: lamellar bases

Make-up

Slight UV protection

Powders

Minerals, pigments

Cutting agents: native flours, polyamides

Powders, compact powder

Slight UV protection

Minerals, healing earth

Are mixed with water before the treatment

Cleansing- and skin care masks

Rinse-off products

Algin, diatomaceous earth

Calcium sulphate; are mixed with water before the treatment

Hardening, occlusive modelling masks (20-30 min.)

Active agents concentrates are applied under the modelling masks

Bromelain, papain; diatomaceous earth, kaolin

Are mixed with water before the treatment

Enzyme peelings (10-30 min.)

Rinse-off products

Soda, citric acid, perfumes or dyes

Binding agent for pills and granules, e.g. starch

Bath additives (sparkling)

Observe pH-value!

¹) Preservatives are listed in the annex of the German Cosmetic Directive (Kosmetikverordnung - KVO). All of them have sensitizing potential.
²) Foaming agents are e.g. saponins from herbal extracts.
³) In presence of unsaturated fatty acids, antioxidants are also used in other forms of application.
⁴) Applications containing phosphatidylcholine (PC) usually are free of preservatives since PC inactivates most of the preservatives listed in the annex of the German Cosmetic Directive. This is an advantage for the microbiome of the skin as it is neither damaged nor can resistances be developed. PC applications hence are particularly suited for sensitive- and problem skin.
⁵) Special forms: multiple emulsions W/O/W and O/W/O
⁶) Physiologically non-degradable emulsifiers lead to washout effects and, depending on their structure and critical micelle concentration (CMC), can also irritate sensitive skin.
⁷) Hypertonia is caused by salts or low molecular, water-soluble compounds such as urea. Hypertonic water phases can also be found in O/W emulsions. In the case of barrier- and connective tissue disorders they can cause a temporary burning sensation on the skin.
⁸) Surface-active semisynthetic or fully synthetic compounds, e.g. sugar tensides. They only gradually differ from emulsifiers due to their usually higher CMC and are preferably used in cleansing products.

From creams to tonics - an overview on different types of applications