Allergic diseases vs. depression. A web of non-obvious links

Allergy and depression – two diseases of the 21st century

Depression and allergy – although apparently so different from each other – share many common factors. Science is investigating whether there is a cause-and-effect relationship between them. Depression and allergies are both diseases of civilisation and epidemics of the 21st century. These diseases are characterised by their global prevalence, and their increasing prevalence is a result of the progress of modern civilisation.

Contributing factors to the increased rate of civilisation diseases include an unhealthy diet, stress, low physical activity, air pollution, and urbanisation [1].

Depression in figures

According to the World Health Organisation, 280 million people worldwide suffer from depression. The disease contributes to more than 700 000 deaths by suicide each year [2]. It is the fourth most common cause of death among people aged 15-29 years [2]. With more than 75% of people with depression in low- and middle-income countries receiving no treatment at all [2].

And what is it like in Poland? After the pandemic, the mental health of Poles deteriorated on an unprecedented scale [4]. One of the factors responsible for this is the phenomenon of pandemic acute stress disorder, which is associated with increased levels of anxiety and distress [4]. Currently, according to the NFZ, approximately 1.2 million Poles suffer from depression [6]. Refunded antidepressants were purchased by 59% more patients in 2021 than in 2013 [6].

Anxiety, stigma, and sense of harm, in other words, between allergy and depression

In recent years, there has been a significant change in the perception of depression, which is referred to by all cases in the media. There are extensive activities such as educational campaigns and depression prevention programmes. However, the disease is still a taboo subject in many circles and often develops in secret. One reason for this is the fear of stigmatisation [1].

Stigmatisation is a phenomenon that is also well known to sufferers of allergic diseases, especially those with skin symptoms. In the course of allergic diseases, the importance of psychological factors is gaining ground. Allergic patients may experience exacerbation of symptoms under the influence of, as one of others, accompanying stress [7]. And the stress factor is also of great importance in the development of depression [8].

It is not uncommon for people with allergies to experience feelings of harm and increased levels of fear of death [13]. It is not helped by the fact that the drugs used to treat allergies, especially if abused or not taken as prescribed, can alter mood and behaviour [8]. They have the ability to indirectly or directly affect the central nervous system [10], as well as a range of side effects. This also gives rise to anxiety, and its dangerous consequence is steroidophobia [13], which is a major impediment to effective treatment. And so the vicious circle closes.

The links between depression and allergic diseases have been the subject of many scientific studies. What do they look like for allergic rhinitis, atopic dermatitis and food allergies?

Allergic rhinitis and depression

Allergic rhinitis (ANN), commonly known as hay fever, is the most common chronic disease in adolescents and young adults, and the most common allergic condition in general [9]. Its symptoms already affect approximately 23-30% of people in Europe and almost 9 million Poles [12]. ANN is extremely bothersome and leads to a significant loss of quality in life [8,10]. It impairs social functioning, contributes to absenteeism from work and school, and handicaps cognitive function. It causes sleep difficulties and increases feelings of fatigue [11]. And this is a straightforward path to mental health problems.

Studies have shown that factors such as stress, mood deterioration and suicidal thoughts correlate with ANN [10]. Because of these correlations, the overlap between allergic rhinitis and depression and suicidal behaviour has been studied [8]. The issue  was recognised as early as in the 1930s. At that time, it was described as “allergic toxemia” characterised by fatigue, psychomotor, and mental retardation, poor memory, irritability, and actually depression [8,12].

Contemporary research suggests that such symptoms are due to the activity of cytokines and other molecules associated with the persistence of inflammation in ANN [8]. There is a clear correlation between an increased and prolonged immune response to an allergen and the occurrence of neuropsychiatric symptoms [12]. Both ANN and depression are associated with activation of inflammatory pathways involving similar mediators [8]. It is presumed that cytokines released during allergic reactions cause neurobehavioural disturbances. And therefore accelerate or persist psychiatric problems, especially depression [8].

There is also evidence of an association between exposure to inhalant allergens and exacerbation of depression [8]. Relevant in this context is the fact that numerous studies on the seasonality of suicides have confirmed the existence of a spring peak that coincides with peak exposure to pollen allergens [8]. In Finland, an analysis of a 13-year database of all suicides was conducted. Among those who committed suicide, a group of people hospitalised for atopy was identified. The analysis indicated that the vast majority of them (78%) had attempted suicide during the pollen season (spring or summer) [8].

Depression in patients with atopic dermatitis

Depression and other neuropsychiatric conditions often coexist with atopic dermatitis. AD is an allergic inflammatory disease affecting 4.7-9.2% of children and 2-8% of adults in Poland [14]. The picture of this disease consists of numerous symptoms, such as the appearance of skin lesions. However, the most significant of these appears to be persistent itching, which dramatically impacts  the quality of life [15]. It causes a scratching reflex that can inflame the skin lesions and lead to their hyperinfection.

The link between AD and the nervous system is already evidenced by the Latin term neurodermatitis, which appears in the scientific literature [15]. Worldwide studies prove  that emotional disturbances can lead to exacerbation of chronic skin inflammation (which occurs in up to 70% of AD patients). They may also result in an increased tendency to depressive states, among others [15]. Moreover, the risk of depression also increases with the severity of the skin lesions. Symptoms manifest themselves most strongly in people with AD symptoms of moderate to severe intensity [15].

Today, it is known that up to 30-40% of people with skin conditions (not only AD) already require psychiatric or psychological care. At the same time, suicidal thoughts were found to be significantly more common in people with AD (18.9%) than in those with contact eczema (5.8%) or urticaria (6.3%) [15]. All skin diseases – whose symptoms are visible to those around them – can result in a sense of stigma and impaired self-esteem [16]. They therefore have a significant impact on the mental state.

The issue of mental health in people with dermatological problems is one of the fastest growing areas of medicine – psychodermatology [15].

Food allergies vs. depression

Psychosocial functioning and quality of life are also significantly impaired by increasingly diagnosed food allergies [17]. They currently affect 4-8% of children and 2-4% of adults [18]. They are usually diagnosed in early childhood and the most common allergens are cow’s milk and eggs [17,18].

The detection of a food allergy in a child alters  the life of the whole family – social gatherings, sleepovers with friends, travel, going out to restaurants, and eating meals in the nursery, kindergarten, or school [17]. Patients with food allergies – or their parents – have to constantly and carefully check the labels of food, medicines, and even toys and personal care products [17]. They face high levels of anxiety and stress daily.

Parents – out of fear of a fatal allergic reaction – find it very difficult to leave their children unsupervised, e.g. in institutions, and drop out of work for this reason. They are excessively vigilant [20]. This in turn becomes an increasing problem as they grow up [17]. These parents, especially mothers, present to doctors with depression and anxiety [20].

And what is it like in children? A study in Italy, among students aged 11-17 years, confirmed that teenagers with food allergies have greater emotional and behavioural difficulties than their peers [17]. In a similar Australian study, adolescents with allergies showed more severe symptoms of depression, anxiety, and ADHD [17]. These students were found to have an increased risk of depression in adulthood. Not insignificant in this context is also the fact that, according to a US study, 24% of food-sensitive allergy sufferers experience allergy-related bullying. Most of these incidents occur at school [20].

At the same time, it has been shown that only 40% of university students with food allergies follow dietary restrictions. Only 6.6% carry an automatic injector with them [20]. Not surprisingly, the risk of death from accidental food ingestion in young adults is increasing [20].

It is also worth mentioning that food allergies increase the risk of not only depression, but also post-traumatic stress disorder (PTSD). PTSD can be triggered, for example, by anaphylactic shock or severe stress related to unexpected exposure to an allergen [20].

Source: pacjent.gov.pl

Aleksandra Lipiec

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translation: Julia Majsiak