Dandruff: A common condition
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At first glance, dandruff might seem like a benign skin condition. But left unchecked, it can have an impact on the health and appearance of your hair. In this article, we provide an overview of what dandruff is (and is not), what causes it and what you can do about excess flakes on your scalp.
What is dandruff?
Dandruff is a common disorder of the scalp characterized by itchy, flaky skin. It has both biological and environmental causes that include abnormal oil (sebum) production, fungal overgrowth and individual predisposition.
How common is dandruff?
Approximately 50% of adults worldwide suffer from dandruff. Like male pattern hair loss, dandruff is a highly visible condition that can have a negative impact on quality of life.
In one large scale study involving 3000 participants diagnosed with dandruff and/or seborrheic dermatitis, quality of life assessments revealed that approximately 80% of questionnaire respondents reported at least some impairment in the areas of symptoms, daily life and interpersonal relationships if they suffered from dandruff. This increased to almost 90% if the individual had both dandruff and seborrheic dermatitis (Szepietowski et al., 2009).
Dandruff tends to begin around puberty and peaks in the early twenties (Borda & Wikramanayake, 2015). The condition is more prevalent in males, which has led some scientists to speculate that male sex steroid hormones may be involved. However, since onset closely follows age, it is more likely that increased oil production plays a role (Manuel & Ranganathan, 2011).
Causes of dandruff
Researchers have identified factors that contribute to the development of dandruff. Sebum production, the overgrowth of fungal species, the health of the outermost layer of skin (also called the epidermis), genetics, pre-existing medical conditions and nutrition are all potentially involved.
Sebum and dandruff
Sebum is the name given to a unique combination of oils and fats that are produced and secreted by human skin. The main purpose of sebum is to lubricate the skin, protect it from abrasion, waterproof superficial layers and protect the body from light radiation. It also possesses antibacterial and anti-inflammatory properties (Makrantonaki et al., 2011).
The production of sebum is partly regulated by male sex steroid hormones such as dihydrotestosterone (DHT). Like the rest of the hair follicle, sebocytes (cells that make up oil-producing glands) produce the enzyme 5-alpha reductase which converts testosterone to DHT. When DHT binds to receptors on sebocytes, sebum production increases (Makrantonaki et al., 2011).
It’s well-known that androgen levels rise sharply around puberty, which can lead to increased oiliness of skin and hair. This is typically accompanied by noticeable flaking and itching of the scalp. However, it’s important to understand that increased sebum production alone does not necessarily cause dandruff and other factors are often involved (Borda & Wikramanayake, 2015).
Fungal overgrowth and the skin microbiome
The surface of human skin is host to a variety of bacteria and fungi. Some of these are capable of causing disease under certain circumstances, while others are commensal organisms that live on the skin. The latter can exist on the skin without causing disease and in some cases, may even be beneficial to health.
An example of a commensal organism is a type of yeast called Malassezia. These yeasts thrive in fat-rich environments and have been implicated in dandruff. However, on its own, the presence of Malassezia on the scalp does not cause dandruff.
Malassezia produces an enzyme called lipase which breaks down fats, including those found in sebum. Although the yeast relies on these fats as a food source, its metabolites (digested products) are potentially damaging to skin. These partially digested fats may interfere with the life cycle and development of certain cells and compromise the outermost protective layer of the epidermis, called the stratum corneum.
As these fats are integrated into the stratum corneum, the percentage and composition of fat in this skin layer changes. This can have consequences on the water content of skin and lead to dryness. Additionally, desquamation (the shedding of dead skin) involves chemical reactions that depend on water to proceed normally (Turner et al., 2012). Therefore, a lack of adequate moisture can have negative effects on cell turnover.
Yeast-digested fats may also cause keratinocytes (keratin-producing cells) to maintain their ability to divide (Warner et al., 2001). Normally, keratinocytes stop dividing as they mature. If cell division is allowed to continue, this increased turnover is a factor in the production of dandruff flakes.
Overall, these changes to the stratum corneum and keratinocytes can trigger scalp inflammation. Abnormal keratinocytes release molecules that prolong an inflammatory response. Some of these molecules also trigger itching, which can aggravate dandruff by causing additional physical trauma to the scalp. A prolonged inflammatory state is damaging to healthy hair follicles and scalp tissues, with negative impacts on hair quality and hair growth.
What other factors contribute to the development of dandruff?
- Medical conditions and treatments that cause dandruff
Studies have found a higher incidence of dandruff and seborrheic dermatitis in individuals with weakened immune systems. This population includes people suffering from certain infections, organ transplant patients and cancer patients.
Scientists theorize that suppression of some parts of the immune system actually leads to overactivation of other parts of the immune system (Wikramanayake et al., 2019). This overcompensation could help explain the increase in pro-inflammatory signalling molecules in the skin of people who have dandruff.
- Is dandruff genetic?
Possibly. Although the inheritance pattern of dandruff is still being explored in humans, animal models have shed light on a few genes that may contribute to the development of dandruff and related skin conditions.
In mice, a mutation in the gene MPZL3 has been linked to abnormal development of the epidermis, which includes the stratum corneum (Borda & Wikramanayake, 2015). In humans, a mutation in the gene ZNF750 has also been associated with abnormal epidermal development, as well as signs of more severe seborrheic dermatitis (Wikramanayake et al., 2019).
- Nutrition and dandruff
The relationship between food and dandruff is unclear, though some studies have found an association between diets high in antioxidant-rich fruit and a reduced risk of developing the dandruff. Meanwhile, diets high in animal-products and processed foods have been linked to higher levels of generalized inflammation (Sanders et al., 2018).
It is difficult to identify a specific nutritional deficiency that causes dandruff. But people who consume foods rich in vitamins and other micronutrients on a regular basis may benefit from their anti-inflammatory properties, broadly.
Are dandruff and seborrheic dermatitis the same thing?
Dandruff and seborrheic dermatitis are closely related dermatological conditions. In fact, some clinicians consider dandruff to be a milder form of seborrheic dermatitis. Both conditions affect the seborrheic regions of the body, or oil-producing areas.
Here are some key differences between dandruff and seborrheic dermatitis:
How to treat dandruff?
Dandruff and seborrheic dermatitis cost Americans hundreds of millions of dollars to treat annually (Borda & Wikramanayake, 2015). This figure includes over-the-counter treatments, as well as prescription medications.
Treating dandruff with medicated shampoos
Dandruff and milder cases of seborrheic dermatitis can generally be treated with over-the-counter hair care products that contain ingredients targeting bacterial and fungal growth such as selenium sulfide, zinc pyrithione or tea tree oil.
Medicated shampoos featuring antifungals such as ketoconazole may also be used (Clark et al., 2015). The frequency of use may need to be determined by a doctor. Additionally, you should be aware that dandruff symptoms may evolve over time and treatment may need to be revised to include both over-the-counter and prescription medications. A doctor or other healthcare professional will make these recommendations, if needed.
Other treatment options for dandruff include shampoos with additives such as salicylic acid or tar. These ingredients can assist with deflaking the scalp (removal of dead skin) and in the case of tar, slow down cell growth. Both of these actions can help reduce flaking and itchiness and provide some relief.
Scalp moisturization and dandruff prevention
Maintaining balanced moisture levels in the scalp is an important part of treating dandruff. When choosing hair or body care products, you’ll want to make sure that they contain effective cleansing agents that don’t strip the skin of natural oils. The scalp should be clean, but not dried out.
Non-foaming or low-foaming products may help minimize irritation, itchiness and tightness (Draelos et al., 2013). You can also look for products that contain moisturizing ingredients such as silicone or plant-derived oils like argan oil to help restore moisture.
Corticosteroids: calming the immune system
Corticosteroids that dampen the immune system and therefore target inflammation may also be considered for severe cases of dandruff. However, there are potentially serious side effects associated with the long-term use of these medications.
Possible side effects of topical corticosteroids include: bruising, thinning of the skin and the formation of stretch marks. A doctor will need to determine whether topical corticosteroids are appropriate to treat your dandruff.
Dandruff is a common condition characterized by an itchy, flaky scalp that can have a negative impact on confidence and self-esteem. It may also be a sign of suboptimal scalp health which has a direct effect on the length, texture and shine of hair. Fortunately, it is a manageable dermatological condition that can be improved with various treatments. If you suspect that you might have dandruff or seborrheic dermatitis, we recommend consulting a doctor or health-care professional for a full assessment and to discuss options for treatment.
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