Skin moisturizers
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Materials needed:
Two clear plastic cups
Water
Felt pen
Cooking oil
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In the United States, billions of dollars are spent each year on lotions and creams to moisturize and relieve dry skin. If you read the labels on several bottles of lotion or cream, you will probably find each contains a number of ingredients, many with long scientific names. Regardless of the ingredients, the way most moisturizing lotions and creams soothe and protect skin is simple, as you will explore in this experiment.

Fill two plastic cups half full with water. Use a felt pen to label one cup A and the other cup B. Also, mark the water level on the outside of each cup. Slowly pour cooking oil into cup B until the surface of the water is just covered with oil. Place both cups in a warm place where they will not be disturbed. Each day for a week, observe how much water is in each cup. What changes do you notice in the water levels during this time? What do you think will happen to the levels after several weeks?

You should find that while the water level decreases in the cup containing only water (cup A), the water level does not significantly change in the cup with the oil layer (cup B). Water easily evaporates from cup A. The thin layer of oil floating on the water in cup B prevents the water in this cup from evaporating.

Water and oil do not mix because their molecules are not attracted to each other. Water molecules are polar and oil molecules are nonpolar. Like molecules attract each other. Unlike molecules have little attraction for each other. Water and oil are unlike molecules.

Water molecules are strongly attracted to each other. This is why water is a liquid under normal conditions. To evaporate, water molecules must have enough energy to escape the attraction of their neighbors. By absorbing heat energy from the room, water in cup A constantly evaporates.

Oil molecules require more heat energy than water molecules to evaporate. Usually, cooking oil will evaporate only when it is heated to a high temperature. This is why the cooking oil does not evaporate from cup B.

Some of water molecules in cup B have enough energy to escape the attraction of their neighbors. When these molecules try to escape, they bump into oil molecules on the surface of the water. They are not able to pass through the layer of oil molecules and do not evaporate.

Moisturizing creams and lotions, which typically contain mineral oil or petroleum jelly, work in much the same way as the layer of oil on the water in this experiment. They help prevent water from evaporating from the skin.

Healthy skin contains about 10% moisture. When skin has a lower moisture content, it becomes dry and flaky. Skin protects itself from loss of water by secreting an oil that forms a film on the skin. This natural skin oil can be removed by exposure to sun and wind as well as by washing. Moisturizing creams and lotions replace the natural oil in the skin and prevent or slow the evaporation of water from the skin.