Human Hands and Fingernails

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The hands are the parts of the human body that is in most contact with the outside world. People use their hands for a variety of activities everyday. It is extremely easy to come in contact with different microbes and to transfer them to other objects and maybe even people. Surprisingly, fingernails harbor the most bacteria found on the human hands.

Description of Niche

Location and Description

The human hands are two prehensile, multi-fingered body parts located at the end of each arm. Normally, a human has five digits on each hand including the following: a thumb, index finger, middle finger, ring finger, and little finger. Fingertips are the areas of the human skin that possesses the highest concentration of touch receptors and thermoreceptors. These dense areas of nerve endings makes the fingers extremely sensitive to heat, cold, pressure, vibration, texture, and moisture. Attached at the distal end of each finger is a fingernail. (7)

Anatomy of the Fingernail
The fingernail is an important structure composed of laminated layers of the protein, keratin (6). Although nails are small, they have :two crucial roles. They act as a protective plate and enhance the sensation of the fingertip by acting as a counterforce. Each nail consists of several parts, including:
Nail Root The nail root is the portion of the nail that is beneath the skin behind the fingernail. It extends several millimeters into the finger and produces most of the volume of the nail and nail bed (6).
Nail Bed The nail bed is part of the nail matrix and extends from the nail root. It contains blood vessels, nerves, and melanocytes. In order to have normal nail growth, it is crucial that the nail bed be smooth (6).
Nail Plate The nail plate is the actual fingernail. It is anchored to the nail bed by the grooves that run along the end of the nail(6).
Cuticle The cuticle of the fingernail is between the skin of the finger and the nail plate. It fuses those two structures together and provides a waterproof barrier(6).
Perionychium The perionychium is the skin that lies over the nail plate on its sides. It is the site of hangnails, ingrown nails, and infection of the skin called paronychia (6).
Hyponychium The hyponychium is the area between the nail plate and the fingertip. This is the area between the free edge of the nail and the skin of the fingertip. It provides a waterproof barrier (6).

Physical Conditions and Changes Due to Environmental Conditions

The skin covers the hand and serves as a layer of protection, sensation, regulation, and control.

Protection It provides a barrier so that pathogens cannot enter the hand freely and also prevents damage between the internal and external environment of the bodily defense system.
Sensation The skin on the fingers of the human hands contain the densest population of nerve endings that may react with heat and cold, touch, pressure, vibration, injury.
Regulation It helps to create an impermeable barrier to fluid loss

The human hand also possesses its own cleaning mechanism. The cells of the epidermis layers of the skin are continually being renewed. In addition, the hand is protected from infection because the skin has fatty acids, components of secretion of the sebaceous glands, and moderate bactericidal properties.

Because the hand is in contact with an infinitive amount of environments and objects, its physical conditions are continually changing. On the human hand, there are resident bacteria that live there all the time and does not cause any harm to the hand. However, because the hands are often in contact with so many different objects, transient bacteria often accumulate on the hands as a result of touching the objects. These bacteria are extremely easy to transfer and may reside on a person’s hand when he/she touches money, food, doorknobs, hair and countless other things. Some transient bacteria may stay on the human hands from minutes to hours or even months. This depends on the type of bacteria that the hand had come in contact with and whether or not they were able to adapt to the physical conditions of the human hands. (10)

There is no “normal” temperature for the human hands. The reason for this is because the temperature of the hands fluctuates and :changes over a certain range of temperatures. The temperature of a “normal” hand can change anywhere from 15.5 to 37.2 degrees :celcius. In the summer, the temperature of the hand will tend to be warmer because blood vessels are nearer to the surface of the :skin. Things such as steroids, tranquilizers, and alcohol will often elevate the temperature of the hands as well. In addition, :coffee, soda, and sugar foods will also have an affect on temperature. Changes of 5, 10, 15 degrees can occur within an extremely :short period of time if the host experiences stress, relaxation, activation of the fight or flight system, or environmental changes. (10)
The normal pH of the hand is acidic (3-5) due to the presence of lactic acid present on the skin from perspiration and the glutamic :and aspartic acids of the epidermis. PH of the skin on the human hands can be altered when it comes in contact with different soaps, :antibiotics, solutions, and hand care. If a very basic solution was used on the skin, then this would cause irritation because it :would be disrupting to the flora of the natural skin on the hands. Therefore, using acidic soaps and antiseptics on the hand is more :beneficial because they are closer to the skin’s physiological pH. When soaps with acidic pH’s are used, they do no interfere :intensely with the microflora of the skin, which has a lower potential to harm the skin. The acidic pH of the skin is also crucial :since the development of many bacteria is strongly inhibited in conditions of low ph than in conditions of neutral to higher pH’s.
The skin on the hands does not like to be too dry or too wet. It is important to keep the hands and fingernails moisturized at a :generally low level to prevent dry skin. Because the moisture level of the skin is generally low, it helps to limit the survival and :growth of microbes. The skin and nails can be damaged by extensive dryness, persistent wetness, cold, chemicals, and sun exposure.  :If grit and soil begins to accumulate on the skin then it begins to lose its protective barrier. With this, water will be lost and :the hands and fingers will become dry. Dryness can create breaking of the skin and make openings that allow contagious germs to enter :and infect. Similarly, fingernails lose elasticity as they begin to lose water. As a result, the nails will be harder and may :crack. The cuticles should also be moisturized as well since they are the seal that prevents moisture from getting underneath the :nail folds. (8)

Different Conditions of the Hand

Unwashed Hands
Contain the natural microflora or resident bacteria and microbes and the transient bacteria from the objects that the hands come in contact with. When the hands are unwashed, there are millions and millions of bacteria living and growing on it (10).
Rinsed Hands
If hands are rinsed with cold water only some large particles of dust and some bacteria is removed but the main majority of pathogens are still there (10).
Washed Hands
Washing hands with soap and water reduces the number of transient bacteria. It is important to remember that it is more beneficial to use soap that is more acidic because the natural ph of hands is acidic. Therefore, the microflora of the hands will not be harmed (10).
Sanitized Hands
When the hands is sanitized, the growth of the bacteria on the hands is stopped and therefore, the majority of the bacteria will be gone.
Effect of Sanitzers Vary
Depending on a person’s normal activities or the job he/she does, the ::::physical conditions of the hands will differ and therefore, the types of bacteria living on the hand will also differ. Ex: Food workers generally have wet hands and their hands are often contaminated with foods in high proteins and fatty acids. This would reduce the effectiveness of the alcohol gel of sanitizers.In addition, the type of soil on a hand affect the significance of sanitizers. Dirt, food, or anything on the hand can make alcohol in sanitizers less effective. (7)

Different Conditions of the Fingernails

Natural Nails
Native nails should be kept clean, short, and should not extend past the fingertips. The subungual region is the site of the majority of the bacteria on the human hands. The growth of bacteria with the nails causes unhealthy, thin, and brittle nails. It is important to take care of the hands and skin surrounding the nails. (9)
Artificial Nails
Artificial fingernails harbor a greater number of pathogens than natural nails. Enhancements of artificial fingernails contribute to the changes in nails that lead to an increase of colonization and transmission of pathogens. Artificial fingernails are made of acrylic. Acrylic is a chemical used to fasten the artificial nail and contains methyl and methacrylate. The acrylic in artificial nails what gives rise to the growth of gram negative bacilli and yeast. Artificial nails are associated with allergies that occur at the time of application of the nail itself. Having artificial nails could lead to a lift in the natural human nail base, therefore, dirt and bacteria will then have the opportunity to invade. Also, bacteria and fungi can also grow in between the natural and the artificial nails. In addition, the cosmetic application of the artificial nail may disrupt the natural environment of the human hands in that it interferes with the skin around the fingernails. The cuticle is the skin of the finger and the nail plate. If too much of the cuticle is cut or pushed back so far that it is separated from the fingernail, this will present the opportunity for infectious agents to move into the area around the fingernails. (9)

Microbes Present

Microbe Genera Found Underneath the Fingernails
Bacteria Fungus Yeast
Pseudomonas Trichophyton Candida
Staphylococcus Epidermophyton Rhodotorula
Acinetobacter Acremonium
Enterobacter Aspergillus
Klebsiella Scopulariopsis
Aeromonas Cladosporium
Staphylococcus aureus. Dennis Kunkel Microscopy, Inc.
There are many species within these genera that can be located within the fingernails, such as Staphylococcus Epidermis and Aeureas or Candida Albicans, Parapsilosis, and Instaniae. These are a select few of the many microbes that can survive on human hands and nails.


Fingernails are increasingly becoming a major concern in many health related issues because of the capability to harbour many varieties of microorganisms. In healthcare related occupations fingernail etiquitte is becoming a strict practice as the bacteria in the nails of healthcare providers can exacerbate a patient's existing medical conditions. This issue is of even greater concern for individuals who have artifical nails. Artifical nails have a greater affinity of harbouring microorganisms than natural nails and have been identified as a major cause of transmitting infections to medical patients. In 1998, a research study was instigated to compare the bacteria found in the nails of various medical staff such as nurses, technicians, and other personel. The study showed that out of all the nails collected (ie. polished nails, natural nails, and artifical nails), artifical nails proved to harbour the most gram-negative rods before and after washing them. Artificial nails have since been scrutinized as having contributed to many hospital acquired infections. In particular, outbreaks of Pseudomonas Aruguinosa have been attributed to two nurses with long, artifical nails and have caused either serious infections or death multiple infants. Also, the Serratia Marcescens bacteria have been involved in the postoperative infections of several cardiac surgery patients.

Fungi and Yeasts

Trichophyton rubrum. Dennis Kunkel Microscopy, Inc.
The hands and fingernails are often affected by fungal and yeast infections, such as those caused by species of Trichophyton and Candida. In particular onychomycosis (nail infection) is the most common disease associated with the hands and feet, effectuating at least 50% of all fingernail infections. Onychomycosis is caused by dermatophytes (infectious fungi or yeast) invading the nailbed, which are also causes ringworms and tinea such as athletes foot. Most cases of onychomycosis is characterized by mild inflamations, resuling in the nail bed becoming cornified and losing its normal contour. Another form of onychomycosis results in the destrcution of the nail plate and is often visible by a whitish yellow discoloration. Onychomycosis can also occur on the external nail plate, caused by an invasion of Acremonium and Aspergillus, which infect the superficial layers of the nail resulting in white patches on the nail. Onychomycosis is increasingly viewed as a major medical concern as these infections can lead to secondary infections as well as being transferred to other bodily areas and other people. Fungi and yeasts are also a major concern for individuals with artifical nails. Artifical nails weaken the natrual and can also cause the natural nail to lift from its base which can expose the fingers to bacteria and fungi that can grow between the nail and artifical nail. These condition substatially increase the risk of onychomycosis and other related diseases. Thus, as mentioned before short cut, natural nails are the best for fingernail health care.

Microbial Interactions

The main mechanism through which microbes interact with each other under the fingernails are through a biofilm. Biofilms are communities of surface attaching microbes that collaborate with each other to perform various tasks that contribute to the community. Often in nature biofilms consists of multiple species of microbes that require inter-species communication. Quorum Sensing is one such method of communicating between cells and species. Quorum sensing is a type of chemical signal that is produced by a community of microbes promoting genetic regulation and cellular changes to bind to e surface and each other. In the fingernails, Candida albicans and [['Staphylococcus aureus]] co-exist in a mixed-biofilm and often cause simultaneous infections. Because they live together in a biofilm it makes it much more difficult to treat infections with antibiotics and antifungals. The resistance is most likely attributed to the biofilm as antibiotic/fungal resistance profiles are often changed in mixed infections. This also makes the microbes capable of persisting many of the conditions hands are exposed to, which is probably why most related infections continue even after washing hands with antimicrobial soap. For example, one experiment introduced a species of Candida into a mixed-species biofilm composed of both yeast and bacteria. The Candida were observed bridging to adjacent colonies and altering its community structure after an acid suppression therapy. The altered biofilm proved to be able to persist in highly acidic environments, surviving in a pH less than three. This implies that biofilms are major mechanisms for protecting microbial communities and are of particular interest for medical concerns as they are indicative of persistence of infections in the human body.

Current Research

‘Super’ bacteria live on sheets, fingernails: study [1]

On June 6, 2005, U.S. researchers reported that MRSA (methicillin-resistant Staphylococcus aureus ) is commonly found on computer keyboard covers and under fingernails which causes rashes and infections. MRSA has resistance to almost everything besides an antibiotic called vancomycin. Vancomycin binds the end of D-ala D-ala which blocks transpeptidation of bacteria to inhibit its growth. Although Staphylococcus aureus is usually harmless and found on skin, it can sometimes cause necrotizing fasciitis or “flesh-eating” disease in hospitals. A study at Northwestern Memorial Hospital in Chicago shows that computer keyboard can contaminate the fingers of a doctor or a nurse, and then further transfer the bacteria to patients thus causing deadly infections.
Fingernails affected by onychomycosis

Onychomycosis due to artificial nails [2]

Although the use of artificial nails is a popular trend nowadays, several bacterial and fungal infections such as Onychomycosis have been found in patients who use artificial nails. Onychomycosis is a fungal infection of the nail which causes 50% of all nail diseases and affects 18% of the general population. Due to the use of artificial nails, Onychomycosis is found to be very common in nail changes. The researchers performed KOH examination and fungal culture to detect the fungal infection from the distal part of the nail and from the proximal nail fold. The results show that both KOH and culture were significantly better in the samples from the distal part of the nail compared to the samples from the proximal nail fold. The study demonstrates that the use of artificial nails can lead to increasing chance of transmitting bacteria. People should avoid using artificial nails especially for health care personnel and food industry workers.

Ultraviolet C inactivation of dermatophytes: implications for treatment of Onychomycosis [3]

In this study, researchers were trying to find an alternative treatment besides antifungals to treat Onychomycosis. The major purpose of the study is to test whether ultraviolet C is able to sterilize a novel ex vivo model of nail infection. Infected human toenail clippings were irradiated with ultraviolet C (254 mm) at a radiant exposure of 36-864 J cm(-2). The results show that ultraviolet C successfully inactivated Trichophyton rubrum and its resistance to ultraviolet C did not increase after five cycles of inactivation in vitro. The radiant exposure might vary depends on the thickness of the vivo culture. Ultraviolet C irradiation might become an alternative treatment for Onychomycosis in the future after researchers find a way to prevent mutations caused by ultraviolet irradiation.

Fast and sensitive detection of Trichophyton rubrum DNA from the nail samples of patients with Onychomycosis by a double-round polymerase chain reaction-based assay [4]

Trichophyton rubrum is one of the pathogens that can be isolated from patients who have Onychomycosis. Using traditional culture-based method to isolate Trichophyton rubrum is a time-consuming process and usually leads to false detection. The study shows it is possible to detect Trichophyton rubrum in fingernail samples using double-round polymerase chain reaction-based assay which is used for DNA detection. The isolated Trichophyton rubrum DNA was amplified using actin gene and internal transcribed spacer 1 in double-round polymerase chain reaction (PCR). The combined detections shows positive results in patients undergo fungal infections. The results suggest PCR is a fast, sensitive and accurate method for fungal detection.

Yale University Experiment [5]

Dr. David Katz of Yale University, the United States, did an experiment with his students to test out the bacteria grow under fingernail. They took swab from under fingernails from different students and let the bacteria to grow. Dr. Katz also took another swab after they wash their hands. After 3 days of growing time, they found out short painted nails have least of bacteria growth. On the other hand, long unpainted nails have most of growth. The reason is because of shorter fingernails are easier to clean. The nail polish is constituted of phthalates, toluene, and formaldehyde which are toxic thus minimizing bacterial growth. The technique of hand washing is also important for limiting bacteria under fingernail. Washing hand properly can kill most of the bacteria under fingernails.


It has been observed that the hands and fingernails are proned to accumulate many different types of bacterial and fungal pathogens. The hands and fingernails are susceptible to different conditions due to the constantly changing environment of the host and of its surroundings. Currently, there is an increasing awareness of hand and fingernail healthcare as healthier fingernails can promote healthier lifestyles.


1. 'Super' bacteria live on sheets, fingernails: study

2. Onychomycosis due to artificial nails. Shemer A, Trau H, Davidovici B, Grunwald MH, Amichai B. J Eur Acad Dermatol Venereol. 2008 Mar 18

3. Ultraviolet C inactivation of dermatophytes: implications for treatment of Onychomycosis. Dai T, Tegos GP, Rolz-Cruz G, Cumbie WE, Hamblin MR. Br J Dermatol. 2008 Jun;158(6):1239-46. Epub 2008 Apr 10.

4. Fast and sensitive detection of Trichophyton rubrum DNA from the nail samples of patients with Onychomycosis by a double-round polymerase chain reaction-based assay. Gupta AK, Zaman M, Singh J. Br J Dermatol. 2007 Oct;157(4):698-703. Epub 2007 Aug 21.

5. Yale Experiment

6. Brannon, MD, Heather. "Nail Anatomy." Dermatology. 24 Sep 2004. 27 Aug 2008 <>.

7. CDC Guideline for Hand Hygiene in Healthcare Settings. Morbidity and Mortality Weekly Reports (MMWR) October 25, 2002.

8. Glove Protects Hands And Fingers In Winter Conditions. ScienceDaily. Retrieved August 28, 2008, from /releases/2003/12/031223073139.htm

9. Kurtzweil, Paula. 1995 Fingernails: Looking Good While Playing Safe. FDA Consumer.

10. Larson, E. 2001. Hygiene of the Skin: When is Clean Too Clean? Emerging Infectious Diseases. 7(2) Mar-Apr 2001.

Edited by [Chao-Lin Chen, Demosthenes Morales, Huynh Nga Vo], students of Rachel Larsen