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Science, Maths & Technology

Rough Science 2 Carriacou: Challenge: Make a sunblock

Updated Monday, 6th March 2017

The science behind sunblocks, tanning and sunburn, and the challenge facing the Rough Science team.

With temperatures reaching 95°F and an unforgiving sun overhead, would botanist Ellen be able to find a natural sunblock to save the scientists’ complexions?

Why does our skin get harmed by the sun?

Three kinds of ultraviolet (UV) light come from the sun:

  • three types of UV rays emitted from the sun Ultraviolet A (UVA) rays are the longest of the three with wavelengths (400-315 nanometers) that penetrate deep into the layers of skin causing tissue damage and wrinkling.
  • Ultraviolet B (UVB) rays have shorter wavelengths (315-280 nanometers) and are known to mainly cause sunburn and skin cancer.
  • Ultraviolet C (UVC) rays are very short (280-100 nanometers) and the ozone layer is designed to protect us from these deadly rays.

How does our skin become tanned?

Tanning shows the reaction of our skin in defending itself against harmful rays from the sun. UVA light stimulates melanin production - and tanning - due to its ability to penetrate into deep layers of the skin.

The melanin in our skin, produced by melanocytes, is a chemical pigment that absorbs UV rays, thus limiting the penetration into the skin tissues. The cells that are hit by radiation are coloured as they move to the surface. When pigmentation disappears, the cells have died. Some people naturally have more melanin in their skin, which protects them a little better than those without much.

melanin defending against harmful rays from the sun

Why does our skin get burnt?

Sunburn is a little different than tanning. Sunburn, also called erythema, is cellular damage from the sun. UVB is responsible for most cases of sunburn and skin cancers. The outer layers of the skin absorb its shorter wavelengths and cause them to burn without stimulating much tanning.

The photochemical reaction causes increased blood flow to the capillaries of your skin. Redness is caused by the extra blood flow. When you press on the sunburnt skin, it becomes white until the capillaries refill.

surface of the skin burning

How can we protect our skin?

Obviously, the best way to protect your skin is by staying out of the sun. Products such as sunscreens and sunblocks will offer good protection from sun exposure.

Sunblocks are different from sunscreens. Sunblocks form a physical barrier to the sun: they are opaque creams or pastes that prevent virtually all light from entering the skin by reflecting and scattering UV rays. They include titanium dioxide, zinc oxide, kaolin, talc or iron oxide.

A sunscreen contains chemicals that absorb the energy contained in the ultraviolet rays and reflect it away as lower-energy long-wave radiation, which is emitted as heat.

sun block versus sunscreen

Did the sunblock work?

the proof it worked On the island, we made a sunblock from kaolin (a fine soft white clay) and coconut oil and also a sunscreen from lime juice. Both proved successful, although we don’t recommend testing these products in the midday sun!



Make Your Own Cosmetics: Neal's Yard Remedies, Aurum Press 1997; ISBN: 1854104691

General information about tropical plants and their uses:

Tropical Forests and Their Crops by Nigel J.H. Smith, J.T. Williams, Donald L. Plucknett and Jennifer P. Talbot, pub Cornell University Press (Discusses general groupings of useful plants)

Botany for Gardeners: An Introduction and Guide by Brian Capon, B.T. Batsford (A good general text on how plants function)

A Field Guide to the Families and Genera of Woody Plants of Northwest South America: (Colombia, Ecuador, Peru): With Supplementary Notes) by Alwyn H. Gentry and Adrian B. Forsyth, University of Chicago Press (An excellent resource on learning to identify tropical plants in the field/forest)

Encyclopedia of Common Natural Ingredients Used in Food, Drugs, and Cosmetics by Albert Y. Leung and Steven Foster John Wiley & Sons Inc

Fruits and Vegetables of the Caribbean by M.J.Bourne, G.W. Lennox, and S.A. Seddon, Caribbean Publishing

Trees of the Caribbean by S.A. Seddon, Caribbean Publishing

Nature of the Islands: Plants and Animals of the Eastern Caribbean by Virginia Barlow, Cruising Guide Publications (This book has all the plants we used, plus information about the ecology of the area.)

A couple of children's books:

The Great Kapok Tree: A Tale of the Amazon Rain Forest by Lynn Cherry, Voyager Books

El Gran Capoquero: UN Cuento De LA Selva Amazonica by Lynn Cherry, translated by Alma Ada, Harcourt





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