Spray Vs. Lotion: The Effect of Sunblock on UVA and UVB

F. Allaire, A. Suenobu, L. Wells PHYS 399 Summer ’09

Ultraviolet Radiation

Ultraviolet (UV) ultraviolet light is the light just past the wavelength of the color violet on the electromagnetic spectrum

UVA frequency ranges 400 - 320 nm

UVB frequency ranges 320 - 290 nm

UVC frequency ranges 290 - 100 nm (these waves are absorbed completely by oxygen and the ozone layer)

UVA –responsible for suntans and

premature aging of the skin and some cancers

UVB associated with sunburns, cataracts and skin cancer

Why should we care about UVA or UVB radiation?

Premature aging of the skin Damaging the skin’s cellular DNA Various forms of skin cancer Eye damage including cataracts Reddening of the skin and sunburn

Protective measures

Wear clothing with Use sunglasses Seek shade Wear hats SPF - Sun Protection Factor

The Skin Cancer Foundation maintains that SPF’s of 15 or higher are necessary for adequate protection.

Purpose

We know that sunscreen does protect. The purpose of this experiment is to determine if there is a difference in effectiveness of protection from UVA and UVB radiation between lotion or clear spray-on sunblock.

Hypothesis

We predict that the lotion would provide more protection than a clear spray-on sunblock of the same SPF value.

Experimental Design

Independent variable: Lotion / Spray-on Sunblock

Dependent variable: UVA, UVB penetration (mW/m2)

Constants: Time of day, amount of sunblock, length of time, SPF, brand, multiple trials using same procedure for each trial,

Control: Clear plastic –no sunblock

Experimental Design

Spray

Lotion

Control

Experimental Design

UVA and UVBProbes and the LabQuest handheld device.

The application of sunblock

Lotion Spray

Setting up in the sun….

Data collection:

Day 1 – Ran 3 trials beginning at 9:55 am until completed.

Day 2 - Ran 3 trails beginning at 10:30 am until completed.

Averages were then made using all 6 trials for the 2 days the experiment was conducted.

We worked carefully to keep all other variables to a minimum.

Variables that could affect results…

Cloudy day!

Variables that could affect results…

The amount of spray:

Two pumps of the spray bottle from the same distance away from plastic!!

Variables that could affect results…

The amount of lotion:

Small amount each time on fingertips applied with the same pressure onto plastic.

UVA:Comparing spray, lotion and control

UVA:Comparing spray and lotion

UVB:Comparing spray, lotion and control

UVB:Comparing spray, lotion and control

Now for some numbers…

UVA UVB

Sunblock Irradiance (mW/m2)

% Total Irradiance (mW/m2)

% Total

Control 7181.645 100 341.9 100

Lotion 159.673 0.022 13.8 0.040

Spray 272.284 0.038 13.3 0.039

Conclusions Our hypothesis was refuted

Difference between spray/lotion and control is significant

Difference between spray and lotion seems insignificant

Wear something!

Extensions Compare brands that have same SPF

value Compare various SPF values Compare time after application Sunblock vs. SPF clothing/sun glasses Effectiveness after water immersion Amount of lotion/spray applied Price vs. effectiveness

Student Research Informal survey: How many students

wear sunblock? Data from this experiment can be used

as a demo to introduce the topic. Students will design and conduct

experiments based on extensions provided in the conclusion.