Combing is part of our everyday life, but have you ever looked at your hair under a microscope?
In this post I present the function, structure and finally the microscopic examination of the hair.
[In this figure] Hair under a scanning electron microscope (SEM) and a compound microscope.
You can see scales (called cuticles) on the surface. Human hair is about 70 microns wide.
photo source:science image
This article covers
the biology of hair
the function of the hair
Hair is a distinguishing feature of mammals. It differs from fish scales and bird feathers. Fur is a thick growth of hair that covers the skin of many mammals. It consists of a combination of moreprotect the hairup and shorterwool hair(also known assub waveor fuzzy hair) underneath. Protective fur prevents moisture from reaching the skin; the undercoat acts as an insulating blanket that keeps the animal warm.
The main purpose of hair is to providethermal insulation🇧🇷 Animals that live in colder climates are usually covered in a thicker layer of fur (also known as fur or wool). For example, the musk ox has dense fur 30 cm (12 in) long. Some desert mammals, like camels, wear thick fur to block solar heat from reaching their skin, keeping the animal cool. Humans, who need little additional protection from the cold due to the development of clothing, are among the least furry mammals.
[In this illustration] The Alaskan musk ox has a very dense coat.
photo credit:Land Administration Office
The skin also acts aswaterproof layer🇧🇷 Aquatic mammals, such as beavers and otters, trap air in their fur to conserve heat, keeping their skin dry.
hair also offersSchutzfor the animals. Porcupines and hedgehogs have their quills, which are hollow hairs hardened with keratin. Fur colors and patterns can be used for camouflage, depending on the animal's habitat. The base of the hair cells is surrounded by nerves, which also makes hair a sensory organ. Bristles are long hairs typically used for visual cues, such as B. a lion's mane.
basic hair structure
A hair can be described as a long, thread-like growth from mammalian skin follicles. A hair mainly consists of a protein, calledkeratin🇧🇷 In detail, the basic structure of hair can be divided into three anatomical regions:Cuticle,Kortex, eBrand.
[In this image] Hair structure: cuticle, cortex and medulla.
Cuticleit is the outer layer of the hair that acts as protective scales. The cuticle consists of overlapping transparent keratin cells. These cells are dead and keratinized, but retain their chemical-resistant keratin fibers and protect the cortex from chemical attack.
The condition of the cuticle determines how smooth and shiny your hair is - because it can be seen and touched. Cuticles can be damaged by chemical processes, excessive exposure to sunlight (UV), excessive heat from the dryer, inadequate brushing and combing, pool water with excess chlorine, etc.
Conditioners just add layers of chemicals to keep your hair soft and shiny. Damaged cuticle cannot repair itself once damaged due to lack of viable cells.
[In this image] The cuticle on the surface determines the condition of the hair.
Kortexit is the main body of the hair and where moisture and natural pigments (called melanin) are held. No other part of the hair has pigment. The amount of melanin contained in the cortex determines the natural color of your hair. Some hair dyes, especially when they lighten the hair, act on melanin. Gray hair lacks melanin.
The cortex consists of elongated, fusiform (spindle-shaped) cells. The cortex may contain air spaces called cortical spindles, pigment grains, and large oval structures called ovoid bodies.
Brandit is the central core of the hair, which may or may not be present. It may be filled with air and then appear as a black or opaque structure in transmitted light from the microscope. When the medulla is present, its structure can be continuous or fragmented. Why this happens has yet to be clarified scientifically.
A schematic diagram of the microstructure of hair. Note that the skin flakes always point from the proximal end or hair root to the distal end or hair tip.
[In this figure] A schematic diagram of the microstructure of hair.
Note that the skin flakes always point from the proximal end or hair root to the distal end or hair tip.
How does a hair grow?
Our hair grows from follicles. Located in the dermal layer of the skin, the hair follicle is made up of 20 different types of cells, each with different functions.
[In this image] Structure of a hair follicle.
We can divide the hair into two parts based on its position. The part of the hair that lies under the skin in the follicle is called the hair follicle.hair root🇧🇷 The base of the hair root is called the hair bulb. The hair bulb is surrounded by blood vessels and receives nutrients for the formation of new hair cells.
When new hair cells form in the hair bulb, the existing hair moves across the surface of the skin and becomes part of the skin.hair shaft🇧🇷 At the same time, these cells also go through a maturation process called keratinization, during which they lose their nucleus (dead cells) and become filled with a fibrous protein called keratin. Hair can therefore be described simply as strands of keratinized protein.
forensic hair science
Trichology is the scientific study of hair. Our knowledge of trichology not only benefits medicine and cosmetics, it is also a valuable tool for forensic scientists to uncover the truth behind crime scenes.
Microscopic examination of hair is a big part of forensic investigations. Just like fingerprints, everyone's hair type is unique. We have soft, medium, hard, thick, thick, straight, curly, damaged and colored hair - with countless combinations of all of them. Hair also absorbs chemicals (like metals) from the environment as it grows. All of these properties can be used in forensics to identify individuals.
Another reason hair is such a valuable tool in forensic investigations is its durability. Hair is more resistant to putrefaction than most other tissues and body fluids and therefore remains intact much longer than other evidence. This durability makes hair one of the pieces of evidence most commonly found at crime scenes.
Forensic scientists perform three main types of hair analysis
The morphology under the microscope
Forensic scientists look at the hairunder a microscopecollect evidence based onMorphology🇧🇷 They usually examine the hair's scale pattern, its color, and the appearance of the spinal cord. An experienced forensic scientist can easily determine whether the hair sample is human or animal. By comparing different hair samples, they can also determine if it's a specific person.
The chemical composition of the hair shaft
Forensic scientists can test thishair shaftfor himchemical composition🇧🇷 For example, chemical analysis of hair can reveal whether the person has used a drug or suffered from nutritional deficiencies. All these evidence can provide valuable information about the hair owner's body condition.
The DNA of the cell in the hair root
forensic scientists can obtaincell DNAat the root of the hair. These DNA samples can provide conclusive evidence about who owns the hair.
[In this illustration] A handy guide and manual used by the FBI for the microscopic analysis of hair tags.You can download and read it on the websitewebsite.
For more details on how forensic scientists work on hair trails at the FBI, follow this link:https://archives.fbi.gov/archives/about-us/lab/forensic-science-communications/fsc/july2000/deedric1.htm
Comparison microscopes, which view two objects (for example, hair or fibers) side by side, are a powerful forensic tool.
A comparison microscope consists of a matched pair of compound microscopes with conventional stages. These steps were connected by a system of lenses, prisms and mirrors in what is known as an optical bridge. The bridge allowed researchers to simultaneously observe and compare two physically separate but optically connected objects in a single field of view. This field of view was divided by a thin optical line.
[In this figure](A) A comparison microscope. Source: Ken-a-Vision Microscopes. (B) An example of directly comparing two hair samples to determine if they are from the same individual. Source:automotive expertise🇧🇷 (C) A split image for firearms investigation. Source: Ludesco Microscopes.
Hair under a stereomicroscope
A stereo microscope is good for the initial examination of the hair before moving on to a compound microscope. Under a stereo microscope, you can easily observe basic features like hair color, shape, texture and length.
Below is an image to remind you of the difference between a compound microscope and a stereo microscope. We also have a post about “How to choose a compound microscope versus a stereo microscope?.“
[In this figure] The difference between compound and stereo microscopes.
Materials you may need:
- Different hair samples - try to collect different types of hair, e.g. B. Human body hair (different body parts), hair from different people, hair from animals such as dogs and cats, etc.
- A stereo microscope (a USB digital microscope will also work)
What can you search?
Using the tweezers, carefully remove the lock of hair and place it under a low power stereo microscope. Observe and see if there are any differences between different hair types.
Under a stereo microscope you should be able to see thatFormhair (straight or twisted, etc.)Corthe lock of hair. If you zoom in you can see them tootexture appearanceon the surface of the hair. When looking at different types of hair, you can also tell them apart based on certain characteristics, such as: B. the thickness between the different strands.
[In this image] Human hair under a stereomicroscope at 5x magnification.
photo credit:world of microscopes
Hair under a compound microscope
A compound microscope has greater power than a stereo microscope to resolve detailed hair structures. However, light must pass through the hair sample to produce a sharp microscopic image. There are two main methods by which different hair textures can be visualized.
Method 1: Make a scale mold with clear nail polish and observe the "microtopography" of the hair
scale castingit is a very useful technique in biology, botany, paleontology and even forensics. Basically, scale casting uses a molding material (such as glue) to create a replica of the surface you want to examine. A good scale cast can show the very fine details of the surface texture (called "Microtopografia') so you can study it under the microscope.
By applying the scale shedding technique to a hair sample, the surface texture of the hair can be well preserved. Since cuticle properties (such as size, shape and arrangement of scales) are the critical characteristics of hair, hair scale scale is very useful for biologists or forensic investigators to identify the origin (human or animal) of hair.
[In this image] An example of flaky hair.
You can see the flaky texture on the surface of the hair.
Materials you may need:
- Nail polish (of course, no preferred color)
- microscopic slides
- tweezers or tweezers
- Various hair samples
- a compound microscope
Follow these steps to scale your slides:
1. Cut the hair sample into 1-2 cm long pieces and keep them handy.
2. Paint a fingernail-sized area with clear nail polish on a blank slide.
Use: Latex (for modeling) can be used instead of nail polish
3. Before the nail polish dries, quickly place the lock of hair in the nail polish area.
4. Let the sheet sit for 10-15 minutes to allow the glaze to dry.
5. When the glaze is almost dry, use tweezers to pull the hair fiber out of the sheet. Hair can sometimes break into pieces when pulled. Okay. Try to pull out as much hair as possible. It is not necessary to remove all hairs.
Use: The enamel/latex is used to attach and hold the scale impression left on the sheet after the hairs have been plucked out.
6. The transparent copy that reflects the hair texture is left on the slide. Your slide is now ready to be viewed!
Note: Although the nail polish is transparent, the surface texture of the hair is preserved. Under a microscope you can see the peaks and valleys that represent the texture of the hair with the shade contrast. Lower light intensity can provide higher contrast and better images.
What can you search?
The scale technique is ideal for lookingouter layer of hairwhich contains thescale(not for the internal structure of the hair shaft). Once the hairs are removed, the scale shapes (or known as "microtopography") remain attached to the slide and can be visualized with a lower magnification lens.
Examine the slide using the low-power objective of a microscope. Look for prints of individual scales. Compare different types of hair and differentiate the characteristics of the scales.
Biologists examine hair prints collected from animals to determine scale patterns. The arrangement and shape of the hair scales can vary greatly from species to species and are often very characteristic. Scientists generally classify scales into two main categories:
- coronary— Completely enveloping the entire width of the hair shaft
- imbricate- Short, wide and not closing the hair shaft
[In this figure] Examples of different mammalian hair cuticle scales.
photo credit:MicrolabNW Micrografias
Try to collect as many hair samples (both human and animal) as possible. Well-made casting blades can be stored in blade boxes (without dust) for a long time. You can create your own library of hair collections.
[In this image] A collection of hair prints from various mammals.
Note that the magnification of each image is different. Also, fur of different types (guard or fur) and body parts can be very different for each animal. More details can be found on this website:MicrolabNW Fotomikrographie-Galerie.
Method 2: Create a full section of hair to observe the internal features (medulla).
A full-frame slide is ideal for viewing the hair's internal structures, such as the medulla.
Materials you may need:
- microscopic slides
- Mounting medium (can be water orWet mounting medium with 70% glycerol)
- tweezers or tweezers
- Various hair samples
- a compound microscope
Follow these steps to create all of your rugs:
1. Cut the hair sample into 1 cm pieces (smaller than the size of the coverslips).
2. Obtain a clean slide and place a drop of mounting medium or water on it. You can learn"how to choose mounting media„
3. Place several strands of hair in the drop of hairspray or water.
4. Slowly lower the coverslip at an angle. Allow one side of the liquid drop to touch the coverslip first. This allows air to escape from the other side.You can use tweezers to help you control the coverslips.
5. Remove excess solution by touching one side of the coverslip with tissue paper.
6. Optional: You can also seal all edges of the cover slip with superglue (or nail polish) to keep the cover slip from moving and for long-term storage.
What can you search?
Examine whole slides first under the low power objectives of a microscope. Once you've found the right focus, switch to high-performance lenses.
Thick hair or dark hair may need a stronger light intensity to illuminate its internal structure. Examine various sources of hair (human versus animal or hair from different areas of the body) and look for different internal characteristics such as grain or airspace. Draw the features of the hair you noticed or take some pictures. You can also measure the width of your hair if you have one.microscopic ruler.
Identify hairs by the appearance of the pith
The medulla is a central nucleus of cells that can be found in the hair. If it is filled with air, it appears as a black or opaque structure in transmitted light.
An entire mount allows the appearance of the cord to be examined; however, a medulla is not always present in a hair (especially in human hair). When piths are present, they usually show marked differences between species. The occurrence of a cord is classified as continuous (uninterrupted), intermittent (regular intervals) or fragmented (irregular intervals).
[In this figure] Diagram of the three basic market types.
The difference in bone marrow between humans and animals
Identifying whether the hair is human or animal is the first step in forensic hair analysis. In human hair, the medullae are generally amorphous in appearance, whereas in animal hair their structures are often very regular and well defined. Human hair usually contains a thin medullary region (less than ⅓ the diameter of the hair), fragmented or absent. Animal hairs usually have thick cords (more than half the diameter of the hair) with regular patterns.
[In this figure] The typical difference in marrow between human and animal hair.
The appearance of the human hair medulla looks fragmented and irregular, while that of the mouse hair medulla contains the periodic pattern.
[In this figure] Examples of different patterns of hair marrow in mammals.
[In this image] A collection of hair pulp samples from various mammals.
The most interesting specimen is the hair of a frozen woolly mammoth discovered in the Siberian ice. Note that the magnification of each image is different. Also, fur of different types (guard or fur) and body parts can be very different for each animal. More details can be found on this website:MicrolabNW Fotomikrographie-Galerie.
Advanced hair biology microscopy
Like other areas of biological research, trichology benefits from advances in microscopic technology. For example, a scanning electron microscope (SEM) can show the detailed surface texture of hair (similar to dandruff, but with much higher resolution).
[In this figure] Scanning electron microscopy analysis of the effect of heat and enzymatic hydrolyzate treatments on hair.
A, B - control; C, D – After treatment with enzymatic and smoothing hydrolysates at 180°; E, F- After treatment with the heat-free enzymatic hydrolysates. Source:BMC Biotechnology.
The combination of fluorescence microscopy and molecular biology gives biologists a great tool to study hair growth, specifically the stem cells that reside in hair follicles. This knowledge can improve our success in treating age-related or disease-related hair loss.
[In this figure] (A) The anatomy of the hair follicle. (B) A fluorescent image of a hair follicle showing two types of stem cells. The colors are marked by antibodies that can recognize specific protein markers on stem cells. Source:development.
Turn your students into a CSI team and use hair analysis to solve a "crime". The forensic mystery will captivate and intrigue them as they learn scientific concepts.
Teaching basic physiological scientific concepts is interesting from a forensic point of view. By incorporating a problem-solving approach into science lessons, teachers engage their students in exciting and innovative ways. Forensic labs also offer “real world” applications of science and mathematics.
„Under the Microscope: Gain Expertise with Hair Analysis”
„History of hair and fiber analysis”
„Identification of human and animal hair”
„Hair, Fiber, Crime and Evidence” by Douglas W. Deedrick. Forensic Science Communication, July 2000 - Volume 2 - Number 3.
How to Choose the Right Microscope (Compound Microscope vs. Stereo Microscope)