Sweat As A Biological Evidence

Sweat is a fluid secreted by the sweat glands also called sudoriferous glands.  The process of production of sweat is called sweating or perspiration. Sweat glands are the  exocrine glands which secretes their production onto epithelial cells by the specific ducts. There are two types of sweat glands :

• Apocrine glands  – they are mostly present at the armpit area, and genital areas.
• Eccrine glands – these glands cover the major surface area of the body. They are present most in the soles and palms then, the head and least in the trunk region.

These two types of gland differ in a number of ways, from distribution and structure, to their excretory mechanism and secretory product .

STRUCTURE OF A SWEAT GLAND

Sweat glands comprise a secretory unit and a duct through which sweat or secretory product is passed. Sweat glands are situated in the dermis and are surrounded by adipose tissue. At the base of each sweat gland there is a structure known as the secretory coil. This is surrounded by contractile myoepithelial cells which act to help secrete the gland’s product. The contraction of these cells are either controlled by hormones or nerve action.

DIFFERENCE BETWEEN ECCRINE AND APOCRINE SWEAT GLAND

FUNCTIONS OF SWEAT

1. Thermo-regulation – It is responsible for thermoregulation. It maintains the temperature by producing cooling effect due to evaporation of the fluid.
2. Lubrication – It is seen that some mammals (eg.dogs, cats, rodents) increase the “grip” of their foot pads during periods of fight-or-flight reaction.
3. Excretory – Through sweat, various toxins are released from the body.
4. Odour – Body odor may occur when bacteria on the skin break down acids contained in the sweat produced by apocrine glands. This odor is sometimes indicative of an ailment and also contains pheromones.
5. Anti-microbial – Sweat contains some endogenous antibacterial molecules, for example dermcidin which has broad-spectrum antibacterial and anti- fungal activity. 

COMPOSITION OF SWEAT

• Majorly water
• trace amounts of lactic acid, minerals and urea.

Mineral contents:

• Sodium (0.9 gram/liter)
• Potassium (0.2 g/ liter)
• Calcium (0.015 g/ liter)
• Magnesium (0.0013 g/ liter)
• Zinc (0.4 milligrams/liter)
• Copper (0.3–0.8 mg/ liter)
• Iron (1 mg/ liter)
• Chromium (0.1 mg/ liter)
• Nickel (0.05 mg/ liter)
• Lead (0.05 mg/ liter )

EXAMINATION OF SWEAT

1. Sweat is one of the biological fluid which exhibits the blood group substances if the person is a secretor, therefore, the analysis of blood group can be done  by examination of sweat. Sweat from secretor individual will contain the Antigens A, B, and H.
2. Odour – A small bit from the suspected sample is taken and heated . The specific odour that comes out is taken note of.
3. Gee’s urea nitrate test – The sweat bearing areas are first examined for the presence of urea by the Gee’s urea nitrate test. If the positive result is found then it is subjected to absorption inhibition, absorption elution or mixed agglutination test for the identification of blood grouping antigens in them.
   
   Procedure
   Stained material is extracted with acetone.
   Now, the acetone extract is set to evaporate to make it more concentrated.
   The residue is mixed with acetone solution in a test tube and mixed with glass rod.
   A slide is prepared with the drop of solution. cover it with the cover slips and prevent overflowing.
   Leave it for few seconds.
   Observe the slide under the microscope.
   Observations:  The crystals appear will have following characterisitics: long, colourless, rhombic shaped.
   

4. Dermcidin Detection- A monoclonal antibody G 81 has been developed which react with dermcidin. Using a Western blot, the G-81 antibody only reacted to the specific peptides in sweat. An antibiotic peptide known as dermcidin is found to have an identical 18-amino acid segment as the N-terminus of a peptide that reacted with G-81. ELISA analysis is able to detect the G-81 reactive peptide in sweat samples subjected to an 8192-fold dilution..

5. SEM coupled with EDX – It can identify the relative concentrations of sodium, phosphorus, sulfur, chlorine, potassium, calcium, and other metal traces. The sweat analysis showed that chlorine and sodium were the only consistently clear peaks among the different samples, and potassium was sometimes visible. The large chlorine peak is used as the basis of comparison and identification

FORENSIC IMPORTANCE OF SWEAT

An average square inch of skin contains 650 sweat glands. That means our bodies leave small amounts of sweat on everything we touch — whether we’re making a phone call, eating supper or committing a crime. Sweat stains become an important biological evidence in cases like kidnapping, sexual assault etc. It can also be present on any kind clothing or on victim’s clothing which can relate us to suspect. It can also be present on surfaces / objects touched by victim or suspect.

Sweat can be analysed for determining ethanol, drugs, ions and metals.

Sweat consists of various biomarkers of different diseases like Cystic fibrosis and diabetes.

SOME INTERESTING FACTS ABOUT SWEAT

• Maximum sweat rates of an adult can be up to 2–4 liters per hour or 10–14 liters per day (10–15 g/min·m²), and is less in children.
• An average square inch of skin contains 650 sweat glands.
• Sweat is moderately acidic to neutral pH levels, typically between 4.5 and 7.0
• Hippopotamus actually produces a red-colored sweat, which acts as an antibiotic and sunscreen.
• A rare condition, chromhidrosis, causes humans to sweat orange, blue or other colors.

To read about New Advancement on Sweat Analysis – Have a look at this research paper, where an assistant professor of Chemistry at the University at Albany, has released a new paper in Analytical Chemistry, which proposes analyzing sweat left behind at a crime scene to determine the number of people who were there .