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9.2 Lifestyle Chemistry: 3. Cleaning products
Syllabus reference (October 2002 version) |
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3. Cleaning products used on the human body must be compatible with the physical and chemical properties of the skin |
Students learn to: |
Students: |
Extract from Senior Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW
Prior learning: Stages 4-5 outcome 4.7 (content: 4.7.5, 4.7.6 c); outcome 4.8 (content 4.8.1, 4.8.3, 8.4.4 and 4.8.5); outcome 5.7 (content 5.7.3).
perform a first-hand investigation to examine prepared slides of human skin
- Perform the first-hand investigation by using a light microscope, at magnifications up to x40, to view some prepared slides of skin tissue such as the following examples, which are available from Southern Biological Services Pty. Ltd., Telephone (03) 9877 4597; facsimile (03) 9894 2309.
- Skin, hair follicles, LS (longitudinal section)
- Skin, scalp, human hair shafts, LS (longitudinal section)
You will need to begin with low power magnification initially, then increase to higher power to make the most comprehensive observations. It will often be necessary to make modifications to the field of view in order to observe and record good examples of the features of skin.
Observe the features carefully and be able to draw and label a representative diagram/s of the skin showing surface features such as hair and pores; the three layers, the epidermis, the dermis and the subcutaneous layer; sebaceous and sweat glands; hair follicles; and blood vessels and nerves.
At school, you may be able to view the slides more effectively using a video-flex camera on a TV monitor or screen. Again, recognise where and when modifications are needed to observe useful sections of skin.
Microscopic sections of skin 
Loyola University Medical
Education Network, Loyola University, Chicago, USA
define the term microflora and discuss the role of the microflora on skin in different parts of the body
- Microflora are microorganisms, including bacteria, fungi, algae, protozoa and viruses, that live in harmless association with our skin. They are able to survive the acidic nature of our skin and sometimes actually help us against the entry of pathogens. Microorganisms that cause disease are referred to as pathogens. The presence of the microflora limits the resources available for pathogenic bacteria that may be able to survive the acidic, salty environment. The microflora also increase the acidic nature of the skin therefore making it even more inhospitable to many pathogens.
- The number and type of microflora found on the skin varies in different parts of the body and between different individuals. The population of microflora of an individual is established soon after birth.
- Some of the microflora that are harmless on the surface of the skin can become quite dangerous if the skin surface is broken and they are able to enter the bloodstream. Staphylococcus aureus can cause serious disease if it gains entry to the bloodstream during medical procedures. Its presence is a serious problem for hospitals and surgeries.
- One species of microflora, Corynebacterium acnes, live in the hair follicles, usually without harm to a person. However, when the dead skin from the epidermis occasionally blocks a sebaceous gland of a hair follicle, the bacteria may infect surrounding tissue resulting in inflammation and causing a pimple.
identify the
role of the skin as
– an organ to separate the body from the external environment
– an organ assisting body temperature control
– an organ to protect against entry by disease-causing organisms
- The skin is an organ to separate the body from the external environment.
The epidermis forms an effective barrier to separate the rest of the body from the external environment. The stratum corneum, which forms part of the epidermis, consists of the dead skin cells that have died from lack of food and oxygen. These dead cells are firmly attached to one another and are keratinised. They protect the living cells beneath them and help reduce water loss. The dead cells flake away and form most of the dust that collects in our houses.
- The skin is an organ assisting body temperature control.
Sweat glands, found in the dermis, produce a liquid that is released through the pores in the epidermis. When this liquid is released on the surface of the body it evaporates and this in turn cools the body surface. When the body becomes hot, the rate at which these glands produce sweat or perspiration increases. As well as this, when the body becomes hot, the blood vessels dilate, which allows loss of heat through the epidermis. These processes help to maintain the body temperature at 37oC.
- The skin is an organ to protect against entry by disease-causing organisms.
The skin protects our body against disease in a number of ways:
- The shedding of the top layer of skin (the stratum corneum) helps prevent the entry of disease causing organisms.
- The film on the surface of our skin, that contains a mixture of sweat, sebum and microflora, is acidic. The acidity comes from the fatty acids that are present in the sebum and from the acids present in sweat. The acidity is increased by the presence of Staphylococcus epidermis, bacterial microflora that break down the fatty acids in the sebum. Many other bacteria cannot survive in such an acidic environment.
- The high concentration of salt in sweat creates an environment that is inhospitable to many bacteria.
- The presence of skin microflora holds in check the small number of pathogenic organisms that are on our skin surfaces. Different parts of the body have different populations of microflora, in balance with the small number of pathogens. This balance can be disturbed by variations in the diet, the use of antibiotics, the use of personal hygiene products and by physical injury.
discuss the term pH in terms of its ability to describe the acidity of a substance
- The pH scale can be used very effectively to describe the degree of acidity of a substance. The pH scale commonly has the range of 0-14, where a pH of 7 is regarded as neutral. Substances with a pH below 7 are regarded as acidic and substances with a pH above 7 are regarded as alkaline. Indicators such as litmus paper, universal indicator paper or universal indicator solution, methyl orange or phenolphthalein can be used to determine the pH of a substance. Alternatively pH meters or probes can be used to determine the pH electronically.
explain
the relationship between the natural pH of the skin and the action of
– microflora
– natural oil produced by glands in the skin
– perspiration
pH and the skin:
- The natural oil in the skin is produced by sebaceous glands and is slightly acidic.
- The sweat or perspiration on our skin is produced by the sweat glands and is also slightly acidic.
- Most bacteria can survive in a narrow pH range. The bacterial microflora on our skin are able to survive acidic conditions with a pH range 4-6. Other harmful bacteria cannot usually survive this environment and so our acidic skin protects us from harmful bacteria or pathogens. Some of our microflora are able to breakdown the fatty acid molecules (from the natural oils) in our skin and thereby increase its acidity.
perform first-hand investigations to measure the pH values of a range of skin and hair products
identify data sources, plan, choose equipment or resources for, and perform a first-hand investigation to test manufacturers’ claim(s) on a commercial product such as soap, shampoo or shower gel and use the available evidence to analyse the results and discuss the validity of the claim(s)
The activities described in the two syllabus points presented above could be done together in the one investigation.
- For this investigation, you need to determine two types of data sources. Firstly you will need to obtain data for manufacturer’s claims with respect to the acidity of their products. This data can be collected from product packaging, product advertising and possibly from the Internet sites of manufacturers. Secondly, you will need to decide what data you will need to collect from your own testing. You must be able to explain the qualitative or quantitative analysis that will be required for this data to be useful.
- You will then need to plan the design of your procedures to allow valid and reliable data to be collected. Below, you will find a basic procedure that you could use to design your investigation, being sure to address the following two considerations.
1. Consider whether your experimental procedure actually tests the hypothesis and which variables you have identified and controlled. You need to be able to identify the dependent variable (the one you observe or measure) and the independent variable (the one you change). Remember, the dependent variable is the variable that responds to changes in the independent variable.
2. Consider the number of trials that are needed to ensure reliable results. (Refer to Reliability and validity - what do they mean?
- Choose equipment appropriate for the investigation. Consider the procedure below for using litmus paper, a pH probe or pH sensor to detect pH values. Be prepared to justify the equipment and technique you choose, including the litmus paper if used.
- Perform the investigation carefully. Test the procedure chosen to determine if it is suitable for the substances you wish to test. Make adjustments if necessary.
- You will need to analyse the evidence available in your results to discuss the validity of the claims made by manufacturers. Make sure that you correctly use scientific principles and ideas and identify any situations where advertised data is incorrect or misleading.
Basic procedures
- Decant small quantities of the liquid substances to be tested into test tubes or beakers. Add small quantities of water to the substances. Test with suitable equipment, such as litmus paper (general), universal indicator paper (more specific) or electronic pH probes. For the substances that are solids, and will not dissolve in water, testing can be done by placing very moist indicator paper onto the surface.
- To test manufacturers claims, use a pH probe or meter to test the pH of substances such as shampoo, conditioner, hair dye, soap, hand cream, deodorant (both underarm and foot) and lipstick. Record the readings in a table such as the one below.
| Skin or hair product | pH reading probe or paper | pH as claimed by manufacturer |
| shampoo | ||
| conditioner | ||
| hair dye | ||
| soap | ||
| hand cream | ||
| deodorant underarm | ||
| foot deodorant | ||
| lipstick |
identify and explain the use of common components of body soaps, cleansers and shampoos and the reason for their use
- The common components of most skin soaps, cleansers and shampoos are surfactants, oils, and fragrances and dyes. The pH of these products should be compatible with that of the skin.
- The surfactants are needed to assist water to attach to oil particles, including sebum that is produced by sweat glands. The surfactant allows water to carry oil and dirt away from the skin surface.
- Oils are included to replace the natural skin oil that is removed by the surfactant in the product. The oils can also protect skin surface or hair from drying.
- Fragrances and dyes are used to make the products more attractive to use.
- Because these products are for use on the skin, the pH of the products must be compatible with that of the skin, which lies in the range 4-6.
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