Which Sunscreen is the Most Effective in Blocking UV Light?

Type (Physical Science, Earth Science, Life Science, Social Science, Mathematics and Computer Science, Engineering, Other)

Physical Science

Grade Level (Elementary, Middle, High School)

Upper Elementary (Grade 5) and Middle School (Grades 6-8)

Difficulty of Project (Easy, Medium, Hard)

Medium Cost

Approximate Cost

$18.00 Excluding the Tri-fold display board

Safety Issues

1. Investigator should not look directly at the Sun while using the UV detector as it may cause permanent eye damage, nor stay exposed to the Sun's ray for a prolong time period.
2. The UV Detector tube contains beads pieces that are small which may be considered a chocking hazard if place in the mouth. Children under 3 years old should not handle the detector tube. Material Availability (Are the materials required readily available?) The UV Detector can be purchased form an online supplier. The various sunscreens and plastic bags can be purchased from the local supermarket or drug store. Also the Tri-fold cardboard display board can be purchased from an arts & crafts store.

Approximate Time Required to Complete the Project (hours, days, weeks)

Less then one day once the materials are secured.

Objective

What is the project about?

The research aspect of this science fair project is to determine the effectiveness of sunscreen lotions in blocking the Sun's ultraviolet (UV) radiation using a UV Bead Detector. Also to evaluate the amount of UVA penetration when using sunscreens with different sun protection factors (SPF).

What are the goals?

The goal of this project is to measure the effectiveness of different sunscreen products for blocking ultraviolet-A (UVA) and ultraviolet-B (UVB) rays from sunlight as indicated by the scale of a UV detection device.

The sunscreen industry markets its products with SPF (Sun Protection Factor) ratings. Sunscreen products of various SPF ratings will be tested for their UV absorbance and effectiveness. Using the data gathered the information will be displayed in a data table and as a graph.

The information gained from this study will be of benefit by presenting scientific data in support of the best SPF rated sunscreen to use to reduce the chances of the harmful effects of ultraviolet radiation over exposure.

Materials and Equipment / Ingredients

What materials are required?

Various sunscreens with SPF values of 10, 15, 20, 30, & 50, box of clear quart-size plastic sealable bags, and a UV Bead Detector.

Where can the materials be found?

The UV Bead Detector can be purchased online from Science in a Bag or Educational Innovations. The sunscreens and plastic bags can be purchased locally.

Introduction

Background information

Earth's atmosphere prevents most ultraviolet (UV) radiation given off by the Sun from reaching the ground the radiation tends to be screened out by stratospheric ozone which is about 35 km above the Earth's surface. UV Radiation has both positive and negative effects. Positive effects of UV radiation include warmth, light, photosynthesis in plants, and vitamin D synthesis in the human body. However, too much exposure to UV causes the skin to burn and leads to wrinkled and patchy skin, cataracts and even skin cancer.

Ultraviolet (UV) radiation is often divided into three different ranges; UV-A, UV-B, and UV-C. UV-A radiation constitutes about 90-95% of the UV radiation that reaches the Earth's surface and can penetrate deeply into the skin leading to cancer and premature skin aging. UV-B radiation does not penetrate the skin as far as UV-A rays but they contain much more energy. UV-B is involved in tanning and sunburn and can cause cellular damage to the skin and eyes. UV-C radiation has the highest energy ultraviolet wavelength but most of it is absorbed by the ozone layer in the Earth's upper atmosphere.

When the human skin absorbs UV radiation, two effects occur. First, melanin (a substance located in skin cells) absorbs as much UV radiation as possible and is changed to a darker color. The second effect is the destruction of the cells responsible for making new cells, or even worse, a rearrangement or chemical change in the DNA within these cells. If these special cells are destroyed, the nervous system sensors are also damaged resulting in pain and increase in the blood circulation in the area producing the characteristic red skin of sunburn. If the DNA is damaged, mutations may occur resulting in age spots, wrinkling, and even skin cancer.

Sunscreen contains ingredients that can absorb and/or filter UV-A light from the Sun so that less of it reaches the deeper layers of the skin. Sun-block, on the other hand, reflects or scatters the UV light away so that it doesn't reach the skin at all. Since the best and most thorough protection comes from blocking both UVA and UVB rays, the ideal sunscreen should be designed to do both. Often, these sunscreens will state that they provide, "Broad-Spectrum" coverage.

Another important factor that needs to be discussed when defining how sunscreens work is the Sun Protection Factor, or SPF. The SPF applies to UV-B rays only, since those are the rays that cause sunburn. Human skin has a natural SPF, partially determined by how much melanin is present in the skin. The SPF is a multiplication factor. If a person can stay out in the Sun 15 minutes before burning, using a sunscreen with an SPF of 10 would allow that individual to resist the sunburn for 10 times longer or 150 minutes.

UV-sensitive beads contain photo-chromatic dyes that react to ultraviolet light and cause the normally white beads to change into vibrant colors when exposed to the sunlight. The UV Detector used in this project contains UV sensitive beads inside of a clear plastic or glass tube. When the detector is shielded from UV radiation, the beads are white. When exposed to UV radiation the beads turn purple. The detector contains a color scale which enables the user to determine the level of UV radiation.

Before having the investigator test the various sunscreen lotions they should view the interactive animation that shows how sunscreen lotion can block UV radiation from penetrating tissue found at the following website.

Diagrams and Pictures

Digital photos can be taken during the experimenting process and an image of the UV Detector can be downloaded from the Science in a Bag website for free and without copyright infringement issues.

The following websites also offer down loadable images of sunscreen products that can be used on the Tri-fold display board: