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## Measuring and Protecting Skin

Author(s): Nancy P. Moreno, PhD, Barbara Z. Tharp, MS, and Judith Dresden, MS.
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#### Session 2: The Law of Nines

1. Explain that, like oranges, our bodies need skin for protection. Mention some of the characteristics of skin: it is the body’s largest organ, provides protection from germs, houses the body’s “cooling” and “heating” systems, contains receptors for our sense of touch, etc.

2. Refer students to the skin diagram on page 8 of this unit's Explorations mini-magazine. Ask, How much skin do you have, and how do you protect it? Have students list the ways they protect their skin, and also record their estimates for the amount of skin on their bodies, in cm2, in their science notebooks.

3. Tell students that the area of skin on the body can be measured with relative accuracy by applying the Law of Nines. This rule of thumb was developed to help doctors estimate the amount of skin damaged on burn victims. Each of the body’s 11 major sections accounts for 9% (or 1/11) of the total amount of skin.

4. Using this rule, students can estimate the total surface area of skin on their bodies by measuring the area of one arm. Working in teams of two, have one student wrap another’s arm in wax paper from the shoulder to the wrist. Have them mark any areas of overlap on the paper, and to avoid including these areas in the estimate of surface area. Then have students switch roles.

5. Have students spread the wax paper “arm wrapping” over two or more sheets of centimeter graph paper and count the number of squares covered. (Or, have older students measure the dimensions of the wax paper and calculate the area as if it were rectangular, or a rectangle and one or more triangles showing area calculations).

6. Once students have calculated the surface area of their arms, have them multiply that figure by 11 to determine the total surface area of skin on their entire bodies.

### National Institute of Environmental Health Sciences, NIH

My Health My World: National Dissemination
Grant Number: 5R25ES009259
The Environment as a Context for Opportunities in Schools
Grant Number: 5R25ES010698, R25ES06932

### Houston Endowment Inc.

Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education