Table 8 Collated potential risk factors for AR presentation

Age

The allergic condition is highest in young adults, declining with age [43]. However, the reason remains unclear.

Alsowaidi et al., 2010 [3]

Li et al., 2015 [22]

Lim et al., 2015 [11]

Ng & Tan, 1994 [36]

Ziyab, 2017 [8]

Li et al., 2014^a [7]

Phathammavong et al., 2008^a [9]

Age of gestation

Preterm baby, who is characterized by lower birth weight and earlier exposure to the mother microflora, have prematurity protection against AR [42]. In contrast, successful pregnancy shifted the T lymphocytes production to Th2 which increases the risk of atopy and AR [22].

Lee et al., 2017 [42]

Li et al., 2015 [22]

Hsu et al., 2009^a [10]

Air conditioning

Home dampness has been shown to be related to allergic rhinitis exacerbations [44], probably in relation to the development of mold or mildew. As air-conditional areas usually have higher dampness, it may lead to increase in AR expression [45].

Phathammavong et al., 2008^a [9]

Zuraimi et al., 2011^a [21]

Air pollution

The pollutants might provoke and exacerbate the allergic conditions of the current patients. Besides, it might also make a person more susceptible to certain allergens [45].

Hsu et al., 2009 [10]

Ng & Tan, 1994^a [36]

Alcohol consumption (self/parent)

Alcohol consumption is related to increased stress level which is one of the provoking factors potentially enhancing AR presentation [2].

Bunnag C et al., 2000 [37]

An et al., 2015^a [2]

Li et al., 2015^a [22]

Birth order

An allergic mother might be more prone to provide low-exposure environment for the next children [29].

Phathammavong et al., 2008^a [9]

Ziyab, 2017^a [8]

BMI

Higher BMI and greater weight-to-height ratio is associated with higher atopic and higher allergic diseases incidence regardless of gender and age [43].

An et al., 2015^a [2]

Lei, Yang & Zhen, 2016^a [40]

Breastfeeding

Breastfeeding for more than 6 months has shown to enhance the presentation of AR [30, 31], but the reason remains unknown. Contrary plausibility has also shown that food proteins consumed by the mother [32] or breastfeeding might help to reduce the inflammatory responses by destroying microbes [33] and is thus protective against AR presentation.

Huang et al., 2017 [34]

Li et al., 2015 [22]

Li et al., 2014^a [7]

Car ownership

Car owners spend more time outdoor and are thus exposed to higher levels of outdoor pollutants [46].

Li et al., 2014^a [7]

Carpet

Having carpets at home increases the risk of accumulating mite allergens, thus resulting in more AR cases [47].

Hsu et al., 2009 [10]

Ng & Tan, 1994^a [36]

Computer usage

Studies suggested that when the computer is not properly cleaned, prolong usage of the computer will likely result in higher allergen exposure and thus an increase in AR cases [7].

Li et al., 2014 [7]

Drinking (self/parent)

Alcohol consumption is related to increased stress level which is one of the provoking factors potentially enhancing AR presentation [2].

Bunnag C et al., 2000 [37]

An et al., 2015^a [2]

Li et al., 2015^a [22]

Education attainment

People with higher education usually work in an indoor environment, thus exposing them to indoor allergens [2].

Alsowaidi et al., 2010 [3]

Min et al., 1997 [20]

An et al., 2015^a [2]

Family history of allergic diseases

Allergic diseases can be hereditary, with incomplete genetic penetrance [48].

Alsowaidi et al., 2010 [3]

Li et al., 2014 [7]

Graif et al., 2004 [38]

Norbäck et al., 2016 (2) [35]

Ziyab, 2017 [8]

Phathammavong et al., 2008^a [9]

Family history of atopy

Atopy is usually used as a marker for other allergic diseases, and genetic factors usually play a role in allergic disease presentation. As such, higher family history of atopy usually suggests higher chance of contracting allergic diseases [43].

Bunnag et al., 2000 [37]

Family size

Crowding increases the contact of an individual with allergens and is thus protective against manifestation of allergic reaction [47].

Li et al., 2015 [22]

An et al., 2015^a [2]

Food

Some foods are protective against AR, most likely through shifting the macromolecules production, such as fatty acid balance, which later results in the reduction of inflammatory mediators required for disease presentation [30].

Phathammavong et al., 2008^a [9]

Fume exposure

Fume released into the air by various means is also one of the potential triggering factors in AR presentation [45].

Ng & Tan, 1994 [36]

Fungi

Airborne fungi spores induce type I hypersensitivity and hence AR presentation [49].

Norbäck et al., 2016 (1) [41]

Norbäck et al., 2016 (2) [35]

Gender

The allergic diseases appear more frequently in males at infant age, but with equal burden as females at mid-teens, and then become more frequent in females with the reason remain largely unknown [43].

Alsowaidi et al., 2010 [3]

Graif et al., 2004 [38]

Hsu et al., 2009 [10]

Lee et al., 2017 [42]

Lei, Yang & Zhen, 2016 [40]

Li et al., 2015 [22]

Bunnag et al., 2000^a [37]

Lim et al., 2015^a [11]

Ng & Tan, 1994^a [36]

Norbäck et al., 2016 (2)^a [35] Phathammavong et al., 2008^a [9]

Ziyab, 2017^a [8]

Gestational complication

Uterus complication during gestation periods affects the immune system development of the fetus and increases the risk of atopy-related diseases [29].

Hsu et al., 2009^a [10]

Gruel introduction period

Study shows that gruel introduction between 4 to 6 months, in complementary with breastfeeding, induces IL-10 and TGFβ production which is protective against AR [34].

Huang et al., 2017 [34]

Hair coloring

Oxidative hair dye can induce hypersensitivity reactions, thus increasing the risk of expressing AR [50].

Li et al., 2014^a [7]

Home renovation

The materials used during the home renovation, such as formaldehyde might have an impact in causing cell sensitization and later AR presentation [7, 31].

Li et al., 2014 [7]

House dust mite

Long term exposure to threshold concentrations of dust mite fecal proteins causes the presentation of allergens by antigen presenting cells (APC) to CD4+ T lymphocytes, leading to the production of downstream mediators and manifestation of AR symptoms [49].

Lim et al., 2015 [11]

Norbäck et al., 2016 (2) [35]

Household income

Higher income is associated with better living conditions and hygiene behavior, thus reducing the exposure to a variety of allergens, which possibly increases their odds of AR [42].

Bunnag et al., 2000 [37]

Li et al., 2015 [22]

Phathammavong et al., 2008 [9]

An et al., 2015^a [2]

Li et al., 2014^a [7]

Housing estate

Living in a housing estate with poor environmental conditions has resulted in more allergic cases [47].

Li et al., 2015 [22]

Ng & Tan, 1994 [36]

Insect

Prolonged exposure to insects, which is one of the common allergens may trigger hypersensitivity reactions with production of mediators and hence, the expression of AR symptoms [49].

Ng & Tan, 1994 [36]

Marital status

Being married is hypothesized to be associated with positive physical and mental outcomes and is therefore protective against AR [2].

An et al., 2015 [2]

Min et al., 1997^a [20]

Maternal education

Educated parents will have higher awareness of their children health status, and thus adopt protective measures to combat against AR starting from a young age [45].

Li et al., 2015 [22]

Hsu et al., 2009^a [10]

Maternal pre- or postnatal depression

Pre- or postnatal depression results in excessive cortisol expression, which will affect the immune system development of the fetus [22].

Li et al., 2015 [22]

Mode of delivery

Exposure of the fetus to the mother microflora during birth is an advantage to protect them against allergic sensitization [29, 51]. In contrast, cesarean birth is associated with higher AR risk [51].

Li et al., 2015 [22]

Ziyab, 2017^a [8]

Mold

Mold spores induce type I hypersensitivity and hence, AR presentation [49].

Kidoni et al., 2004 [19]

Hsu et al., 2009^a [10]

Nationality

AR prevalence is especially high in Asia probably due to the higher humidity, more extensive smoking and vaccination habits [43].

Alsowaidi et al., 2010 [3]

Occupational exposure

Some occupations have higher risk of exposure to allergens, thus increasing their risk of expressing AR [50].

An et al., 2015 [2]

Ng & Tan, 1994 [36]

Min et al., 1997^a [20]

Parasitic infection

Parasitic infection might have some effects to a person’s gut microbiota, which could later offer some protection against allergic sensitization as stated in hygiene hypothesis [52]. However, some literature also show that parasitic infection influences the allergy development due to its competition with human immune response [9].

Phathammavong et al., 2008 [9]

Parity

Being allergic might cause reduced reproductivity in females, resulting in a lower parity which is associated with AR presentation [29].

Hsu et al., 2009 [10]

Phathammavong et al., 2008^a [9]

Past measles infection

The association of measles with AR is not clear, but it was hypothesized that measles infection might protect against AR development or could promote allergic sensitization [52].

Phathammavong et al., 2008^a [9]

Past respiratory infection

Evidence shows that past respiratory infection, such as tuberculosis caused by Mycobacterium tuberculosis could be protective against AR, possibly through reduction of allergy sensitization [52]. In contrast, some studies have shown that past respiratory infection is directly associated with AR development [9].

Phathammavong et al., 2008 [9]

Paternal education

Educated parents are more likely to keep a hygienic living environment, thus possibly increasing the incidence of allergic conditions in their children [45].

Li et al., 2015 [22]

Pet

For individuals sensitive to pet furs, long term exposure to the pet induces hypersensitivity reaction and could later result in AR presentation [49].

Li et al., 2014 [7]

Ziyab, 2017 [8]

Phathammavong et al., 2008^a [9]

Hsu et al., 2009^a [10]

Lim et al., 2015^a [11]

Ng & Tan, 1994^a [36]

Race

Cultural differences between the races probably have some effects on AR presentation; however, there is currently no specific research addressing the impact of races on AR disease presentation.

Graif et al., 2004 [38]

Ng & Tan, 1994 [36]

Norbäck et al., 2016 (2) [35]

Residency

For people who lived in urban areas, they are more prevalent in developing allergic reaction [47], probably due to a poorer housing or environmental conditions. Modern building techniques increase indoor humidity and temperature, facilitates mold development and hence, contributes to AR presentation [2].

Graif et al., 2004 [38]

Lee et al., 2017 [42]

Li et al., 2014 [7]

Min et al., 1997 [20]

An et al., 2015^a [2]

Sharing bed

Sharing bed is hypothesized as one of the potential risk factors for AR [9], probably due to increased risk of getting infections from other people.

Phathammavong et al., 2008^a [9]

Sleep time

People with lesser sleep are usually with higher levels of stress, which is a potential trigger factor for AR expression [2].

An et al., 2015 [2]

Smoking (self/parent)

Tobacco smoke is one of the trigger factors which precipitates the hypersensitivity reactions, thus exacerbating the AR conditions [47]. On the other hand, parents with AR children will also try to reduce their children exposure to external allergic stimuli through changing their smoking habits, thus explaining the negative association of AR and smoking habit [45].

Bunnag et al., 2000 [37]

Li et al., 2014 [7]

Ng & Tan, 1994 [36]

Zuraimi et al., 2008 [39]

An et al., 2015^a [2]

Hsu et al., 2009^a [10]

Li et al., 2015^a [22]

Lim et al., 2015^a [11]

Min et al., 1997^a [20]

Norbäck et al., 2016 (2)^a [35]

Phathammavong et al., 2008^a [9]

Ziyab, 2017^a [8]

Social class

As stated in hygiene hypothesis, people in lower social class are likely to have a greater exposure to infections. This may have direct and indirect impacts to their gut microbiota, which might offer protection against allergic sensitization [45, 52].

Min et al., 1997^a [20]

Stress level

Stress can trigger the production of cortisol, and later induce allergic responses [28].

An et al., 2015 [2]

Time on road

Longer time spent on road is associated with higher AR risk, probably due to prolonged exposure to air contaminant [9].

Phathammavong et al., 2008^a [9]

Traffic

The release of motor vehicles such as NO_x and CO provokes and exacerbates the conditions of the current AR patients, and might have consequences on changes in susceptibility towards allergens, thus affecting AR presentation [45]. Depending on the outdoor environmental pollution, long term exposure to heavy traffic might lead to allergic sensitization and resulted in AR expression [21].

Zuraimi et al., 2011 [21]