What are the Definitions for Different Topical Substances?

Patient Presentation
A 7 month-old male came to clinic with dry itchy skin that has been worsening over the past week.
His mother says that he has had dry skin before but not this bad and she has never put anything on it.
She has noticed that it is worse on his arms, legs and face but he has dry skin in general.
He has been itching more and she noticed that his elbows, knees and cheeks appear more reddish.
The family history shows that mother has dry skin, with ‘bumps’ on her upper, outer arms and thighs.
The pertinent physical exam reveals a healthy male with generalized dry skin that is mainly papular with areas of lichenification and hypopigmentation over his body.
He has areas of excoriation in the flexural areas of the elbows and knees, on his cheeks and behind his ears.
These areas are also more pink-red in color than the surrounding skin. He has no areas that appear infected.
The diagnosis of atopic dermatitis was made. His mother was educated as to the natural history of the disease.
She was told that she could bathe him frequently with a mild ‘beauty bar” such as Dove® or a non-soap alternative such as Cetaphil®.
She was told to pat him dry and to use “thick” emollients such as petrolatum to protect his skin. She was told to use to use the emollients every couple of hours to keep his skin moist.
She was also told to use thinner emollients, such as a cream or lotion, if he was going to be in a warm place so he wouldn’t sweat under the emollients and irritate his skin.
She was also instructed on the signs of infection, and the importance of applying sunscreen too.

Atopic dermatitis or eczema is a common dermatological skin problem which characteristically is a pruritic, papular eruption with erythema.
Sometimes atopic dermatitis is described as the “itch that rashes.”Rubbing and scratching can lead to excoriation and, over time lichenification.
There can also be secondary infections or changes to the skin pigmentation (hyper- or hypo-) in affected areas.
Emollients for skin rehydration are a mainstay of treatment. Topical steroids are commonly used to decrease inflammation in affected areas.
Immunosuppressants such as tacrolimus are also used in some cases.

Learning Point
The definitions of common topical substances are:

  • Ointments- Its base is an oil (a hydrocarbon). It may have the ability to have a water incorporated into it making a water-in-oil emulsion. One example is Aquaphilic®.
  • Creams – Its base is water. It may have the ability to incorporate an oil into it making an oil-in-water emulsion. These are easier to wash from the skin and therefore people may like them better than ointments.
  • Gels – Its base is water and fine particles are more or less permanently suspended in the liquid. The number of particles is so great to render the liquid into a semi-solid state.
  • Lotions – Its base is water with fine particles more or less permanently suspended in the liquid. The particle numbers are so few that the liquid remains a liquid.

Each of these topical substances has different properties which affect how it acts on the skin.
How long a topical substance remains on the skin depends on many factors including the substance applied, amount applied, the location, rubbing of the location, occlusion of the area, contact with other substances such as water, sweat, etc.
Although I cannot reference a specific amount of time, I have been taught that the approximate time topicals stay on the skin is:

  • Ointments- 2 hours
  • Creams – 1 hour
  • Gels/Lotions – 20-30 minutes

One gram of a topical ointment or cream covers approximately 10 x 10 centimeters of skin. A 30-60 gram tube should cover the entire skin of an adult once.

Questions for Further Discussion
1. For liquids, what is the difference between a suspension and a solution?
2. What are the indications for using immunosuppressants for atopic dermatitis?
3. What is keratosis pilaris?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Information prescriptions for patients can be found at MEDLINEplus for this topic: Eczema

To view current news articles on this topic check Google News.

Stedman’s Medical Dictionary. 24th Edit. Williams &Wilkins. Baltimore, MD. 1982.

Berkowitz CD. Pediatrics A Primary Care Approach. W.B. Saunders Co. Philadelphia, PA. 1996:392-396.

Robertson J, Shilkofski N. The Harriet Lane Handbook. 17th. Edit. Mosby Publications: St. Louis. 2005:977,1031.

ACGME Competencies Highlighted by Case

  • Patient Care
    1. When interacting with patients and their families, the health care professional communicates effecively and demonstrates caring and respectful behaviors.
    2. Essential and accurate information about the patients is gathered.
    3. Informed decisions about diagnostic and therapeutic interventions based on patient information and preferences, up-to-date scientific evidence, and clinical judgment is made.
    4. Patient management plans are developed and carried out.
    5. Patients and their families are counseled and educated.

    8. Health care services aimed at preventing health problems or maintaining health are provided.

  • Medical Knowledge
    10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.
    11. Basic and clinically supportive sciences appropriate to their discipline are known and applied.

  • Practice Based Learning and Improvement

    13. Information about other populations of patients, especially the larger population from which this patient is drawn, is obtained and used.

    Donna M. D’Alessandro, MD
    Associate Professor of Pediatrics, Children’s Hospital of Iowa

    June 12, 2006