Lotion

Key takeaways

Lotion belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lotion to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lotion from memory before moving on to harder problems.

Reference excerpt

Lotion is a low-viscosity topical preparation, typically an emulsion of oil and water, intended for application to unbroken skin for moisturizing, protective, cosmetic, or medicinal purposes. By contrast, creams and gels have higher viscosity, typically due to lower water content. Lotions are applied to external skin with bare hands, a brush, a clean cloth, or cotton wool. While a lotion may be used as a medicine delivery system, many lotions, especially hand lotions and body lotions and lotion for allergies are meant instead to simply smooth, moisturize, soften and sometimes, perfume the skin.

Medicine delivery

Dermatologists can prescribe lotions to treat or prevent skin diseases. It is not unusual for the same drug ingredient to be formulated into a lotion, cream, and ointment. Creams are the most convenient of the three but inappropriate for application to regions such as the scalp, while a lotion is less viscous and may be readily applied to these areas (many medicated shampoos are in fact lotions). Historically, lotions also had an advantage in that they may be spread thinly compared to a cream or ointment and may economically cover a large area of skin, but product research has steadily eroded this distinction. Non-comedogenic lotions are recommended to put on acne- prone skin. Lotions can be used for the delivery to the skin of medications such as:

Antibiotics Antiseptics Antifungals Corticosteroids Anti-acne agents Soothing, smoothing, moisturizing or protective agents (such as calamine) Anti Allergens

Occupational use Since health care workers must wash their hands frequently to prevent disease transmission, hospital-grade lotion is recommended to prevent skin dermatitis caused by frequent exposure to cleaning agents in the soap. A 2006 study found that application of hospital-grade lotion after hand washing significantly reduced skin roughness and dryness. Care must be taken not to use consumer lotions in a hospital environment, as the perfumes and allergens may be a danger to those who are immunodeficient or with allergies.

Cosmetic uses Most cosmetic lotions are moisturizing lotions, although other forms, such as tanning lotion, also exist. Cosmetic lotions, including products marketed for anti-aging, often contain fragrances or other ingredients intended to modify the appearance or feel of the skin. The Food and Drug Administration voiced concern about lotions not classified as drugs that advertise anti-aging or anti-wrinkle properties.

Production Most commercial lotions are oil-in-water emulsions — where oil droplets are dispersed in water — stabilized by emulsifiers such as cetearyl alcohol. Water-in-oil lotions, in which water droplets are dispersed in oil, are also produced and have different sensory and absorption properties. The key components of a skin care lotion, cream or gel emulsion (that is mixtures of oil and water) are the aqueous and oily phases, an emulsifier to prevent separation of these two phases, and, if used, the drug substance or substances. Various other ingredients such as fragrances, glycerol, petroleum jelly, dyes, preservatives, proteins and stabilizing agents are commonly added to lotions. Manufacturing lotions and creams can be completed in two cycles:

Emollients and lubricants are dispersed in oil with blending and thickening agents. Perfume, color and preservatives are dispersed in the water cycle. Active ingredients are broken up in both cycles depending on the raw materials involved and the desired properties of the lotion or cream. A typical oil-in-water manufacturing process may be:

Step 1: Add flake/powder ingredients to the oil being used to prepare the oil phase. Step 2: Disperse active ingredients. Step 3: Prepare the water phase containing emulsifiers and stabilizers. Step 4: Mix the oil and water to form an emulsion. (Note: This is aided by heating to between 110 and 185 F (45-85 C) depending on the formulation and viscosity desired.) Step 5: Continue mixing until the end product is 'completed'

Potential health risks Lotions are generally considered safe for typical cosmetic or therapeutic use, but certain formulations or usage patterns can be associated with adverse effects, including irritation, increased absorption of active ingredients, hospitalization (if swallowed), or allergic reactions.

Acne Depending on their composition, lotions can be comedogenic, meaning that they can result in the increased formation of comedones (clogged hair follicles). People who are prone to acne or forming comedones often prefer lotions that are designed to be non-comedogenic (not causing outbreaks).

Systemic absorption All topical products, including lotions, can result in the percutaneous (through the skin) absorption of their ingredients. Though this has some use as a route of drug administration, it more commonly results in unintended side effects. For example, medicated lotions such as diprolene are often used with the intention of exerting only local effects, but absorption of the drug through the skin can occur to a small degree, resulting in systemic side effects such as hyperglycemia and glycosuria. Absorption through the skin is increased when lotions are applied and then covered with an occlusive layer, when they are applied to large areas of the body, or when they are applied to damaged or broken skin.

Allergens Lotions containing some aromas or food additives may trigger an immune reaction or even cause users to develop new allergies. There is currently no regulation over use of the term "hypoallergenic", and even pediatric skin products with the label were found to still contain allergens. Those with eczema are especially vulnerable to an allergic reaction with lotion, as their compromised skin barrier allows preservatives to bind with and activate immune cells. The American Academy of Allergy, Asthma, and Immunology released a warning in 2014 that natural lotion containing ingredients commonly found in food (such as goats milk, cow's milk, coconut milk, or oil) may introduce new allergies, and an allergic reaction when those foods are later consumed. A 2021 study found that "frequent skin moisturization in early life might promote the development of food allergy, most likely through transcutaneous sensitization".

Illustrations

Worked examples

Example 1 — a first encounter with Lotion

Start with the simplest possible case. Write down what Lotion claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lotion before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lotion ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lotion

In research: Lotion appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lotion in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lotion is common in secondary-school and first-year university syllabi. It links to neighbouring topics Dosage forms, Drug delivery devices, Emollients and protectives, so understanding it makes those chapters shorter.
In everyday life: Look for Lotion outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Lotion in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lotion means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lotion out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lotion in simple terms?

Lotion is a low-viscosity topical preparation, typically an emulsion of oil and water, intended for application to unbroken skin for moisturizing, protective, cosmetic, or medicinal purposes. By contrast, creams and gels have higher viscosity, typically due to lower water content.

Why does Lotion matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lotion?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lotion.