CHAPTER 10
Creams and Ointments

Irwin Palefsky

Cosmetech Laboratories, Inc., Fairfield, NJ, USA

Definitions of creams (and lotions) and ointments

Creams (and lotions)

Creams (and lotions) are emulsions. While this may seem very basic it is important that we understand what an emulsion is, the different types of emulsions and the role that they play as a vehicle and delivery systems for functional and drug active materials.

In looking for a generally accepted definition I came across the following: “In classic terms, emulsions are colloidal dispersions comprising two immiscible liquids (e.g. oil and water), one of which (the internal or discontinuous phase) is dispersed as droplets within the other (the external phase) [1].” What is missing from this definition is the inclusion of the emulsifier(s) or dispersing agent(s) that are responsible for keeping these two immiscible phases together for an extended period of time. All emulsions are inherently unstable – they will eventually separate into two or more phases. The determination of what to call an emulsion – a cream or lotion – is usually guided by the viscosity. If an emulsion has a relatively low viscosity, flows with gravity and can be poured out from a bottle, or pumped out, it is usually described as a lotion. If the emulsion has a high viscosity, requires a jar or a tube, and does not readily flow with gravity, it is usually referred to as a cream.

In this chapter, we will use the term emulsion to refer to creams and lotions.

The other part of a definition of an emulsion is based on the materials that make up the internal phase and the materials that make up the external or continuous phase. The two primary categories of emulsions are oil‐in‐water (O/W) and water‐in‐oil (W/O) emulsions (Figure 10.1). The names themselves describe the composition of the emulsion.

The predominant types of emulsions used in topical dermatological formulations are O/W emulsions. These emulsions are generally defined by their emulsifier type, i.e. anionic, cationic, and nonionic. This terminology refers to the ionic charge (or lack of charge) on the emulsifier system that is predominant in the emulsion.

We also have O/W emulsions that are based on polymeric emulsifiers and “liquid crystal” emulsifiers. In all cases, these emulsions hold the two phases (oil and water) together and prevent them from separating by different mechanisms from those seen in traditional emulsions, which use more conventional emulsifying systems.

The term “natural” emulsions have become a category that consumers are interested in using.

The term “natural” is subject to different definitions and for the most part natural ingredients are derivatives from a plant, tree or nonpetrochemical source, and natural emulsions generally refers to emulsions based on these ingredients and the composition of these emulsions are primarily made up of “natural” emulsifiers and emollients. For more information on this I refer you the chapter on pharmaceutical emulsions and micro‐emulsions in the book Pharmaceutical Dosage Forms: Disperse Systems, Volume 2, edited by H.A. Lieberman et al. published by Marcel Dekker, Inc., 1996.

Schematic illustration of different emulsion types. — **Figure 10.1** Different emulsion types.

W/O emulsions are becoming increasingly popular as emulsion types for dermatological products and OTC sunscreen products. In W/O emulsions, the “oil phase” is the external phase. Because of this, W/O emulsions have always been assumed to be “heavy” “oily’ formulations. Today, with newer emulsifier technology and increasing interest in w/o emulsions, it has become more possible to develop formulations with a wider variety of feel and esthetics. As such it has become increasingly popular for delivering enhanced skin barrier protection, water resistance, and a more effective delivery system for hydrophobic (i.e. oil soluble) ingredients. The technology has dramatically improved so that one can now develop W/O formulations that have a high degree of consumer/patient acceptance and are not greasy or oily.

Ointments

In searching for a definition of an ointment the best one that I came up with was on the Internet: “Semisolid preparations used topically for protective emollient effects or as a vehicle for local administration of medicaments; ointment bases are various mixtures of fats, waxes, animal and plant oils, and solid and liquid hydrocarbons”[2]. This definition is as comprehensive as any I have seen. Because ointments are traditionally anhydrous bases they pose less microbial contamination issues than emulsions, which generally contain water (either in the internal phase or the external phase). In addition, because they are anhydrous in nature and are a combination of water insoluble components, they tend to be more water resistant than emulsions. Ointments tend to have less aesthetic appeal for skin care/dermatology products that need to be used on a regular basis or for an extended period of time. Ointments are frequently described as “oily,” “waxy”, “greasy,” “sticky/tacky,” and “heavy.” They do however have a more medicinal connotation and do find functionality and effectiveness when developing treatment products for the lips and anhydrous semisolid systems.

Composition of a cream and an ointment

Oil‐in‐water cream

The most popular type of emulsion used in everyday skin care products and in “cosmeceutical products” is an O/W emulsion. A generic composition for an O/W emulsion is shown in Table 10.1 [3].

Table 10.1 Composition of a typical oil‐in‐water emulsion.

Ingredients	% (weight/weight)
Water phase
Deionized water	60.0–90.0
Humectant	2.00–7.0
Preservative^a	0.05–0.5
Water soluble emulsifier^b	0.25–2.5
Thickener(s)	0.1–1.0
Water soluble emollient	0.5–2.0
Chelating agent	0.05–0.20
Oil phase
Emollient system – oils, esters, silicones, etc.	3.0–15.0
Oil soluble emulsifiers	2.0–5.0
“Active ingredients”	As required by regulations
Oil‐soluble antioxidants	0.05–0.5
Fragrance/essential oil etc.	0.1–2.0
Color	As required
pH adjustments	As required