The hair is distinguished by its simple structure; Where it consists of keratin , which is a type of strong and strong protein in the body, and living cells are found in the hair bulb, which is the base of the hair , and its cells are nourished by the blood vessels that transport food and hormones that affect hair growth During the different stages of life. The cells grow in the hair follicle to give the hair shaft which is anchored and fixed on the hair follicle until it leaves the skin. And the hair passesDuring its life in three phases; The hair growth phase , which lasts for several years, then the regression phase where hair growth becomes slow during these weeks, then the telogen phase where hair growth stops, separates from the follicle and falls to allow For a new hair to start its life stages. 
Hair analysis that scientific examination is conducted for a sample of hair , whether those found in the crime scenes or those taken from the head in order to health studies,  as well as possible through hair analysis knowledge of relatives, check Cases of mineral poisoning, and a hair analysis gives an idea of the changes occurring in the body. Such as exposure to certain chemicals or taking a type of drug during the past few months, while not giving information about the recent changes that occurred during the past days due to the slow growth of hair. 
The scientific principle of poetry analysis
The hair can keep a long-term record of what the body was exposed to from drugs, drugs, and minerals during the life of the hair estimated at five to six years, as the analysis depends on examining the hair itself, the fatty substances surrounding it, and the deoxyribonucleic acid . The analysis is based on a simple principle; It is that the hair during its life and growth inside the hair follicle absorbed many substances in the bloodstream, and this process continued and the hair started to grow and grow and record what it contained in the blood throughout its life, and these substances are also found in the fat layer surrounding the hair which was secreted from the sebaceous glands : Sebaceous gland). 
How to do hair analysis
There is a set of laboratory instructions for preparing a hair sample for examination, and in general the hair should be clean and free of hair care products, then the sample is taken from an area close to the skin where this area of the new hair is growing to give up-to-date information about the body, and it is usually taken The sample is from the bottom of the scalp or from the pubic area, then the sample is sent to the laboratory to be treated with certain chemicals and then examined. 
The following is a simple explanation of the hair analysis techniques used: 
- Trichogram technique: This technique is based on the principle of physical examination with the naked eye , and by using a microscope for the hair and scalp, and this technique is currently used to find out the life phase of the hair and determine the cause of hair loss.
- Gas chromatography / mass spectrometry: This is where the chemical examination of the hair is done to find out the components of DNA, minerals, drugs, drugs, toxins , and heavy metals present in the hair, even if they are in small and simple quantities.
Uses of hair analysis
Here are some of the possible uses of hair analysis:
Examination of minerals, drugs and toxins
Hair analysis can be used to check poisoning with heavy metals such as lead , mercury , and arsenic . Hair analysis is the typical medical examination for chronic arsenic poisoning . Mostly from farmers inhaling insecticide sprays. Hair analysis can also be used to confirm the presence of narcotic substances, such as cocaine , or hashish , or alcohol, or amphetamines (amphetamines), or one of their metabolites , and it is worth noting that the results of this test need three Weeks to appear, and its results are always approved in the courts if the need arises.  
- External factors; Such as the place of residence or work may cause a false positive result , as it happens when a person is near another person who smokes marijuana or hashish.
- There is no standard examination method; Which leads to the emergence of different results between laboratories, and even in the same laboratory, different results may appear when analyzing more than one hair of the same sample, which makes it necessary to confirm the result through a blood test or urine test .
- Not knowing the relationship between the amount of drugs or alcohol consumed and the amount that will appear in the hair.
- Use of some types of medicine; Such as birth control pills, which can change the concentration of minerals in the hair.
- Exposure to hair lotions; Such as shampoo, bleaching, and hair dyes can reduce the proportion of some minerals as can deposit other minerals.
- Other factors such as; Age, gender, hair color, ethnicity, rate of hair growth, and the location from which the hair was sampled, all of these can affect the concentration of elements in the hair.
Forensic DNA examination
To perform this examination, the hair must be plucked or pulled from its place instead of cutting it, and this may cause some pain,  in order to preserve the hair root for use in the analysis of the hair's DNA Whereas, the DNA fingerprint is used as conclusive evidence in crimes, and it is also used in forensic medicine to confirm whether a person has been addicted to alcohol or drugs during the past month or months, based on the length of the hair that was examined. 
A healthy body evaluation and disease diagnosis
Although some research indicates that hair can be analyzed to find the level of the hormone cortisol. As some studies have indicated a possible relationship between its elevation and heart disease, diabetes, stroke, and other diseases,  but hair analysis for this purpose is not reliable. It often raised controversy, and it is worth noting that most insurance companies do not pay for this type of hair analysis, and the claim of some laboratories, medical sites, and health care facilities is considered the ability of hair analysis to diagnose diseases, evaluate the nutritional and health status of a person, and determine the need and deficiency of the body from Minerals and elements are false claims that cannot be trusted.  
Reasons for uncertainty in analyzing hair for disease diagnosis:
- The American Medical Association indicated that the internal health of the body is not related to the chemical and physical state of the hair .
- This examination may have errors due to the failure of the laboratories to verify the conformity of the techniques used for them to the approved standard reference.
- The natural values of minerals in hair have not yet been determined.
- Difficulty using hair analysis to diagnose the disease, due to slow hair growth as it grows at a rate of 1 cm per month, and therefore even the hair closest to the scalp will be several weeks old, and thus it does not reflect the health situation at this moment.
- Matthew Hoffman (11-3-2017), "Picture of the Hair" , www.webmd.com , Retrieved 1-10-2017. Edited.
- Susan Vinoth Pandian (1-3-2016), " the Analysis Hair: Your Hair Tells The Truth About You ... But Not All Of It" , Www.medindia.net , Retrieved 1-10- 2017. Edited.
- Healthwise Staff (21-8-2015), "Hair the Analysis" , the www.webmd.com , Retrieved 29-9-2017. Edited.
- Robert Preidt (17-4-2013), "Seriously Stressed? Hair Analysis May Tell All" , ww.webmd.com , Retrieved 1-10-2017 . Edited.
- Stephen 's. Barrett (28-5-2017), "Commercial Hair the Analysis" , Www.quackwatch.org , Retrieved 1-10-2017. Edited.