For many people, the scalp is hidden under hair, so it is not a cause for much daily concern. Rarely are consumers complimented for a beautiful scalp. However, attention should be paid to it.
The scalp is the soft tissue envelope of the cranium. It is the anatomical area bordered by the face at the front and by the neck at the sides and back. There are five layers to the scalp; the first and outermost one being the skin.1 This unique part of the body is both an extension of the face and often a concentrated area for hair growth. In fact, the proximate structural arrangement of the scalp and hair leads to an interdependent relationship between the two.2 Thus, maintaining a healthy scalp is important not only in and of itself, but also for healthy hair —which is additionally an important factor for physical well-being.3
The present article serves as a primer on scalp biology, potential scalp skin conditions and formulating strategies to maintain a healthy scalp.
The scalp skin is thick and contains a high density of hair follicles and numerous sweat and sebaceous glands. These glands have an important physiological role. They produce sebum that is released via sebaceous ducts to the skin surface. This is the body’s natural moisturizing oil and it keeps the scalp skin and hair lubricated. Sebum comprises a mixture of lipids such as triglycerides, fatty acids, wax esters and squalene cholesterol, as well as the debris of lipid-producing cells.4
Another important physiological component is the outermost layer of the scalp skin, the epidermal stratum corneum. It consists of cells that are mostly dead and ready to be shed to reveal the newer layers of skin beneath. The detachment of the dead cells from the surface is a normal part of the cell cycle and is usually invisible.
Together, the stratum corneum and sebaceous glands protect the scalp from various factors. Just like the stratum corneum of the body, scalp stratum corneum serves as a barrier against external insults, e.g., the pathogenic invasion of microorganisms, oxidative stressors, UV irradiation, air pollution, etc., thus maintaining homeostasis between the external environment and internal tissues. It also acts as the primary epidermal barrier to water loss, maintaining healthy hydration and integrity of the scalp.5 As noted, sebaceous glands produce sebum, which has antimicrobial properties, providing another layer of protection against scalp conditions caused by bacteria and fungi.6
The scalp has an average normal pH between 4.5 and 5.5, and maintaining this acidic pH is important for skin health. The specific anatomic features of the scalp skin include a large number of hair follicles—on average, 100,000;7 an enlarged epidermal surface due to numerous hair canals; sebum content; moisture; and an acidic pH contribute to a specific microenvironment of the scalp and higher rate of exfoliation.1, 8
A healthy scalp also requires a balanced microbiota. In fact, the physiologic functions of the scalp, such as skin barrier function, production of sebum and regeneration of the follicle, can be regulated and affected by the scalp microbiome.9-11 And although, as noted, sebum has antimicrobial properties, some microbes manage to thrive in this environment. Cutibacterium (previously Propionibacterium), for example, hydrolyzes triglycerides and releases free fatty acids, promoting its adherence and contributing to the acidic pH of the skin surface. Also, Malassezia spp. and Corynebacterium spp., which do not produce their own lipids, may benefit from lipids of the sebum as a nutrient source.12
Disturbances to a healthy scalp can cause certain conditions such as scalp dryness, mild irritation, itch, scaling, inflammation, hair thinning and even hair loss. Modifications to the scalp stratum corneum can be caused by harsh cleansers, for example. The sun may also damage stratum corneum cells, as could external factors including air pollution, allergens, cold weather, cooling and heating—especially in highly contained living environments. Additionally, internal triggers, such as stress13 and diet via the skin-brain-gut axis, can disturb and damage the scalp.
In certain scalp conditions, such as with increased Malassezia yeast density levels14, 15 and a weakened skin barrier,16 skin cells multiply more quickly than usual, cellular masses form—i.e., hundreds or thousands of cells per square centimeter;14 and the detachment of dead cells from the scalp surface becomes visible in the form of flakes (dandruff).
Sebaceous gland activities can also lead to scalp and hair conditions. If these are reduced, they produce a small quantity of sebum and the hair will be dry. If their activity is high, producing larger amounts of sebum, the hair will appear greasy, and this can also lead to a sebum build-up within the scalp pores. If hair follicles clog, they form red bumps. The excess use of some hair care products, including heavy styling products, without cleansing in between styles can also cause build-up and can clog the follicle, which can impact healthy hair growth and lead to breakage.2
- Tajran, J. and Gosman, A. (2020, Jan). Anatomy, head and neck, scalp Available at https://www.ncbi.nlm.nih.gov/books/NBK551565/
- Trüeb. R., Henry, J., Davis, M. and Schwartz, J. (2018, Nov-Dec). Scalp condition impacts hair growth and retention via oxidative stress. Int J Trichology10(6) 262-270.
- Gokalp, H. (2017). Psychosocial aspects of hair loss, hair and scalp disorders Available at: https://www.intechopen.com/books/hair-and-scalp-disorders/psychosocial-aspects-of-hair-loss
- Picardo, M., Ottaviani, M., Camera, E. and Mastrofrancesco, A. (2009, Mar-Apr). Sebaceous gland lipids. Dermato-Endocrinology1(2) 68-71.
- Turner, G., Hoptroff, M. and Harding, C. (2012). Stratum corneum dysfunction in dandruff. Intl J Cos Sci34, 298-306.
- Rattanakaemakorn, P. and Suchonwanit, P. (2019). Scalp pruritus: Review of the pathogenesis, diagnosis, and management Available at: https://www.hindawi.com/journals/bmri/2019/1268430/
- Gilaberte, Y., Prieto-Torres, L., Pastushenko, I. and Juarranz, A. (2016). Anatomy and function of the skin. In Nanoscience in Dermatologypp 1-14. Elsevier, Amsterdam.
- Xu, Z., Wang, Z., Yuan, C., et al. (2016). Dandruff is associated with the conjoined interactions between host and microorganisms. Scientific Reports6 24877.
- Beri, K. (2018). The scalp microbiome: A look at future applications for scalp and hair cosmetics and new avenues for personalized treatment. EURO Cosmetics4 16-20.
- Saxena, R., Mittal, P., … Sharma, V., et al. (2018 Oct). Comparison of healthy and dandruff scalp microbiome reveals the role of commensals in scalp health Available at: https://www.frontiersin.org/articles/10.3389/fcimb.2018.00346/full
- Grimshaw, S., Smith, A., Arnold, D., Elaine, X.E., Hoptroff, M. and Murphy, B. (2019, Dec 18). The diversity and abundance of fungi and bacteria on the healthy and dandruff affected human scalp Available at: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0225796
- Polak-Witka, K., Rudnicka, L., Blume-Peytavi, U. and Vogt, A. (2020). The role of the microbiome in scalp hair follicle biology and disease. Exp Dermatol29 286-294.
- Chen Y. and Lyga J. (2014). Brain-skin connection: Stress, inflammation and skin aging. Inflammation & Allergy - Drug Targets13 177-190.
- Schwart, J., et al. (2013). A comprehensive pathophysiology of dandruff and seborrheic dermatitis – Towards a more precise definition of scalp health. Acta Derm Venereol93 131-137.
- Ranganathan, S. and Mukhopadhyay, T. (2010). Dandruff: The most commercially exploited skin disease. Indian J Dermatol 5(2) 130-134.