Covid 19 was a systemic viral illness that started in 2019 and took over the world soon after. This resulted in international borders being shut down, and people asked to quarantine in their houses. Millions of people all over the world were affected by the infection caused by this virus. Even if the majority of these individuals recovered completely, the virus leaves certain long-lasting results on the body, including a change in taste, change in smell, and hair fall. This article explores how the covid 19 virus may lead to hair fall, as reported by a good percentage of people diagnosed with it.
Dr. Reena Jogi is a dermatologist who specializes in PRP Hair Restoration in Houston, Texas.
The Covid 19 virus, which may adobe referred to as SARS COV 2, has often been linked to significant hair weakening and hair fall. A major cause of this hair fall has been proposed to be associated with the stress caused by the virus, which can weaken the hair follicles. After the fever starts, the individual may start experiencing hair loss within 3 to 4 months of the infection. This is because the cytokines get released in the body as soon as the fever start, which causes the conversion of follicles prematurely to catagen and telogen.
Since the telogen is the phase of hair cycles that has a duration of 4 months, the hair present in the telogen phase starts shedding off as soon as it completes. There are numerous ways through which SARS COV 2 virus may cause injury to the hair follicles. These include direct injury of hair follicles, Antibody associated injury, cytokine-associated injury, apoptosis-associated injury, and microthrombi-associated injury. (1)
Covid 19 associated direct injury to the follicles is due to the cell damage caused by the SARS COV 2 virus. This cellular damage is usually caused by the direct interaction of the virus with the ACE 2 receptors, through which it enters the cells in the basal layers of cell follicles. (2) However, there is still a need for more studies to determine the extent of injury to hair follicles that the covid 19 virus is able to cause directly.
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Another pathway through which covid 19 may increase the incidence of hair fall is through antibody-dependent enhancement. (3) (4) In a healthy individual, when the virus infects an individual, the antibodies present in the body can usually neutralize this virus and prevent the spread of infection. However, when the antibodies are sub neutralizing in nature, they may enhance their entry into the cell rather than blocking it. This will cause a greater replication of the virus and lead to the phenomenon known as an antibody-dependent enhancement. This mechanism was previously commonly seen in certain strains of dengue infections, after which it was later observed in the Covid 19 infections. The anti-body-dependent enhancement usually works by interaction with FC or complement receptors, which are commonly expressed in the human hair follicles and keratinocytes. This involvement of the hair follicles is hypothesized to be linked with hair fall. (5)
Viral infections like Covid 19 cause the release of a large number of cytokines in the body, as a antiviral response. These commonly include TNF Alpha, IL-1, IL-6, IL-1β, IL-8, IL-12, GM-CSF, and interferon-gamma. (6) These pro-inflammatory factors have the ability to directly impact the dividing keratinocytes and papillar cells of the skin. For example, the Tumor Necrosis Factors and IL-6 are two types of pro-inflammatory factors which are found to have an inverse relationship with the growth of hair follicles. On the other hand, the factor IL-4 is often seen to increase in the elderly population, as it is linked to the cell death of keratinocytes. (7)
This association has been investigated in numerous studies as well. One such study was conducted on 543 post covid patients in Wuhan. After three months of follow-up, alopecia was observed in at least 154 of these patients. While the majority of these patients reported starting experiencing alopecia after being released from the hospital, some started experiencing hair loss during their hospitalization. (1)
The hair damage caused by cytokines has also been previously reported in cancer patients undergoing chemotherapy and radiotherapy. It is suggested that it may not only be the increased exposure to cytokines that may be causing damage to the hair follicle resulting in hair fall, but the nutritional deficiencies during the infection period may also play a role. This is especially true for hospitalized patients who cannot consume food on their own.
The endothelium contains the receptors known as ACE2, through which the virus is able to gain access to the cells. The inflammation caused by this process can lead to the t helper cells releasing many cytokines and recruiting Eosinophils. Other immune cells that may also be released due to this inflammatory response include the cytotoxic t cells, b cells, and natural killer cells. The release of all these immune cells leads to the development of lymphocytic thrombophilic arteritis.
This is further proven by histopathological test on the covid 19 patient, which has shown their skin lesion to contain large numbers of white blood cells along with infiltrates of plasma and intraluminal thrombi. These blood clots or thrombi that form in the microvasculature are associated with the lack of blood supply to the hair follicles. The reduced blood supply can interrupt the oxygen transport to these structures, creating a hypoxic environment, which may cause damage to the hair follicles - ultimately leading to hair fall.
Hair fall, which may also be referred to as Telogen Effluvium, is commonly seen after viral infections like Covid 19. This is most commonly encountered during the post-recovery period due to factors like direct injury to hair follicles, microthrombi associated injury, cytokine associated injury, and due to a phenomenon known as an antibody-induced enhancement.
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