Author (Year)	Study Type/ Sample Size	Study Objective	HS Severity	Results	Limitations
Psychological Stress
Chiricozzi (2018)[@167648]	Cross-sectional questionnaire/ 86 hidradenitis suppurativa (HS) patients 100 obese individuals 85 control subjects	Assess the presence of alexithymia in patients with HS	Not applicable	The mean Toronto Alexithymia Scale (TAS)-20 score was significantly higher in the HS patient cohort (55.37 ±13.42) than in the control group (40.96±10.47) (p < 0.001)	Cross-sectional design
Esmann (2011)[@167650]	Interview/ 12 HS patients	Assess the psychosocial impact of HS	Not applicable	HS negatively impacts self-worth, intimate relations, communication, and work. It also leads to increased stigmatization	Small study sample Descriptive analysis
Frings (2019)[@167645]	Questionnaire/ 110 HS patients	Assess the psychological burden in HS	Hurley Staging	Significant correlation between Hospital Anxiety and Depression Scale and Visual Analogue Scale (VAS) (for pain) (p = 0.009), between Skindex-29 and Sartorius score (symptoms: p = 0.024; emotions: p = 0.019), as well as between Skindex-29 and VAS (symptoms: p = 0.000; emotions: p = 0.001)	Small study sample
Gielin (2020)[@167641]	Case-control/ 71 HS patients and 213 controls	Assess the link between traumatic events and the development of HS	Not applicable	Childhood emotional traumatic events (odds ratio (OR) 5.03, p < 0.05) were significantly associated with the development of HS	Recall bias Small study sample
Keary (2020)[@167649]	Structured interview/ 12 HS patients	Assess the psychological distress in HS	Not applicable	HS patients commonly experience shame and pain and have adapted coping mechanisms to deal with their symptoms	Small sample size Descriptive analysis
Kirby (2017)[@167651]	Cross-sectional, multicenter survey/ 154 HS patients	Investigate resilience, depression, and health-related quality of life (HRQOL) in HS patients	Not applicable	The resilience score was significantly associated with depressive symptoms (regression coefficient a = −0.21; p < 0.001), and the depressive symptoms score (c = 0.637; p < 0.001) was significantly associated with lower HRQOL (c′ = 0.644; p < 0.001)	Cross-sectional design
Kouris (2016)[@167643]	Questionnaires/ 94 HS patients	Evaluate quality of life, depression, anxiety, loneliness, and self-esteem in patients with HS	Not applicable	HS patients presented with significantly higher anxiety (6.41 ± 3.31 vs. 5.00 ± 1.59, p < 0.001), depression (5.45 ± 2.79 vs. 4.16 ± 1.54, p < 0.001), loneliness and social isolation scores (42.86 ± 8.63 vs. 35.57 ± 6.17, p < 0.001) and lower self-esteem scores (18.91 ± 1.79 vs. 19.77 ± 2.53, p = 0.008) than controls	Small sample size Self-reported diagnoses
Matusiak (2010)[@167646]	Questionnaires/ 54 HS patients	Assess the psychophysical aspects of HS	Not applicable	Advancement of the disease is the most important factor negatively influencing patients’ well-being (P < 0.01). The anogenital location appears to impair the HS patients’ quality of life most of all (P < 0.05), but the occurrence of lesions on uncovered skin plays a large role in the stigmatization level (p < 0.05)	Small study sample
Tzur (2020)[@167647]	Population-based retrospective review/ 4,191 HS patients 20,941 controls	Association between bipolar disorder and HS	Not applicable	Higher bipolar disorder HS patients compared with controls (0.7 vs. 0.1%,)	Retrospective design
Mechanical Stress
Boer (2015)[@167654]	Case study/ 1 HS patient	Resolution of HS by dietary measures	Not applicable	A 33-year-old female with chronic HS experienced resolution of the induration of her lesions on her inner thighs and lower abdomen corresponding to the location of her waist band, but persistent lesions on her buttocks after a 32 kg weight loss	One patient No controls/interventions
Boer (2016)[@167652]	Case study/ 1 HS patient	Elucidate role of mechanical stress in HS	Not applicable	33-year-old woman with HS had superficial nodule and follicular papules in area of mechanical stress by bra edge	One patient No controls/interventions
Boer (2017)[@167655]	Case series/ 14 HS patients with lesions in areas exposed to	Describe possible Koebner phenomenon in HS	Not applicable	All patients were obese with mean BMI of 35.8 and had ectopic HS lesions at the sites of friction of the convex abdomen (waistband)	No controls/interventions
De Vita (2018)[@167657]	Case study/ 1 HS patient	Elucidate role of mechanical stress in HS	Not applicable	54-year-old man without a history of HS developed chronic, recurrent, inflammatory nodules, cysts, and depressed scars at the location of a giant abdominal hernia	One patient No controls/interventions
de Winter (2012)[@167656]	Case study/ 1 HS patient	Elucidate role of mechanical stress in HS patients	Not applicable	44-year-old man without a previous history of HS had recurrent, inflammatory deep-seated nodules, abscesses and fistulas on the amputation stump of his left leg, at the site of his lower leg prosthesis	One patient Lack of intervention Case study design
Dufour (2010)[@167658]	Case study/ 1 HS patient	Possible influence of mechanical stress on the development of HS	Not applicable	Infant developed HS-like lesions in inguinal naevus comedonicus after mechanical stress in the area	One patient No controls/interventions
Rondags (2017)[@167653]	Case study/ 1 HS patient	Elucidate role of mechanical stress in HS	Not applicable	28-year-old man with a history of HS developed small ulcers with yellowish-brown discharge and sinus tract formation as well as a dark erythematous plaque on his right foot after wearing a new, rigid pair of tight-fitting work shoes	One patient No controls/interventions
Von Der Werth (2004)[@167644]	Cross-sectional questionnaire/ 156 HS patients	Describe natural history of HS	Not applicable	16/110 (16%) patients reported tight clothing and friction as an aggravating factor of HS and 11/110 (11%) reported loose clothing as a relieving factor of HS	Recall bias
Sleep
Cohen (2021)[@167664]	Retrospective study/ 4,417 HS patients and 22,085 controls	Determine the association of HS and obstructive sleep apnea (OSA)	Not applicable	Patients with HS have a 1.60 OR of having OSA (95% CI 1.36-1.86; p < 0.001) and a 1.32 OR of having a non-OSA sleep disorder (95% CI 1.12-1.57; p < 0.001)	Lack of data on severity of HS
Kaaz (2018)[@167660]	Cross-sectional questionnaire/ 108 HS patients and 50 controls	Pain and itch sleep implications in HS patients	Hidradenitis Suppurativa Score (HSS) Hidradenitis Suppurativa Severity Index (HSSI) Hurley’s Staging	Mean± standard deviation The Athens Insomnia Scale (AIS) and Pittsburgh Sleep Quality Index (PSQI) scores among patients with hidradenitis suppurativa vs. controls were assessed as 5.4±4.3 vs. 5.5±3.4 and 6.5±3.6 vs. 3.1±1.9 points, respectively. The presence of itch and pain had a significant impact on the frequency of insomnia.	Cross-sectional design
Kelly (2021)[@167662]	Prospective study/ 36 HS patients and 31 psoriasis patients	Formal sleep studies to assess OSA prevalence in HS	Hurley Staging	50% HS patients and 34% psoriasis patients had a high probability of OSA, as assessed by the Berlin and STOP-Bang questionnaires. Six patients with HS (37%) and six psoriasis patients (43%) were positive for sleep apnea based on overnight sleep studies.	Small study sample
Vossen (2017)[@167661]	Cross-sectional/ 211 HS patients	Prevalence and characteristics of pruritis in HS patients	Not applicable	121/211 (57.3%) of patients had pruritus based on a numerical rating scale (NRS, 0 – 10) with a mean NRS score of 6.1 ± 2.0	Cross-sectional design
Wertenteil (2018)[@167663]	Retrospective cohort analysis/ 19,945 HS patients	OSA incidence in HS	Not applicable	OSA incidence among patients with HS was 3·5% (n = 695/19 945) vs. 2·5% (n = 7400/296 170; p < 0.001) in patients without HS. The overall odds of a new OSA diagnosis among patients with HS were 1·41 [95% confidence interval (CI) 1.30–1.53] vs. without HS 1.45 (95% CI 1.33–1.57)	Retrospective design
Smoking
Akdogan (2018)[@167637]	Case control/ 40 HS and 40 control	Smoking and its risk with HS	Hurley Staging HS Physicians Global Assessment (PGA)	Smoking associated with a 14.87-fold increase in the risk of HS (p = 0.001, 95% CI 2.82—78.56)	Small sample size
Deilhes (2020)[@167665]	Retrospective review/ 51 HS patients who smoked	Smoking cessation program (SCP) vs. smoking reduction program (SRP)	Not applicable	48 patients followed up for 11.6 months, with 70% of patients attending the SCP. 1/3 stopped smoking and 44% reduced consumption (mean decrease 2.4 cigarettes per day). Among quitters, 93% attended the SCP.	Lack of controls Descriptive analysis
Denny (2017)[@167638]	Retrospective review/ 198 patient smokers and non-smokers	Assess patient factors that increase response to medical therapy	Not applicable	Non-smokers/former smokers had a 2.634 (95% CI = 1.301-5.332, p = 0.007) times increased odds of having improvement in their disease compared to current smokers, regardless of amount smoked	Study design Lack of controls
Dessinioti (2017)[@167666]	Retrospective review/ 133 patients with HS	Association between smoking and HS severity	Hurley Staging Number of affected areas in the body	Smoking causes no change in Hurley staging (OR = 1.31, 95% CI: 0.37–4.61), but increases number of affected body areas (OR: 3.56, 95% CI: 1.27–9.96)	Small sample size Retrospective design
Dessinioti (2018)[@167673]	Retrospective review/ 186 patients with HS	Association between early-onset HS and smoking	Hurley Staging Number of affected areas in the body	Early-onset HS (<17 years old) is associated with fewer smokers than adult-onset HS (p < 0.001)	Recall bias Small non-smokers sample size
Foolad (2021)[@167682]	Cross-sectional review/ 761 patients with HS	Characterize patients with HS at University of California Medical Center	Not applicable	There was a prevalence of about 38% current or former smokers in the cohort, and 57.7% of never smokers	Lack of confounder analysis Data from online database
Garcovich (2021)[@167679]	Cross-sectional review/ 870 pediatric patients with HS	List risk factors for hospital-based pediatric patients with HS	Hurley Staging	23.9% of the cohort were smokers which is higher than the referenced general population of 11.8%	Cross-sectional design Small sample size Generalizability limitations
Garg (2018)[@167667]	Retrospective review/ 7,860 HS patients	Incidence of HS among tobacco smokers	Not applicable	Incidence of HS was 0.20% among tobacco smokers and 0.11% among nonsmokers (p < 0.001)	Cross-sectional design
Iannone (2021)[@167680]	Retrospective cohort/ 36 patients with moderate-severe HS	Evaluate the effects of smoking on response to antibiotic therapy for HS	mSartorius, acne inversa severity index (AISA), DLQI	Smoking was positively correlated with AISA (Spearman's rho = 0.51, p = .036) and DLQI (0.47, p = 0.061) in patients being treated with clindamycin and rifampicin.	Small sample size Retrospective design
Killasli (2020)[@167678]	Cross-sectional registry/ 1,724 pregnancies with HS, 13,538 patients overall	Study the prevalence of lifestyle factors that negatively affect health and pregnancy in HS pregnant patients	Not applicable	Smoking was reported in 41% of pregnant women with HS. 13% of women in the reference group were smokers.	Cross-sectional design Missing variables for some patients
Kjaersgaard (2021)[@167669]	Prospective cohort/ 23,930 Danish blood donors	Association of remission rates of self-reported HS with smoking	Not applicable	Smoking was statistically associated with the development of self-reported HS (HR = 1.72, 95% CI: 1.15-2.5). Active smoking was also statistically associated with remission rates. (HR = 0.49, 95% CI: 0.32-0.76)	Self-reported diagnosis
Kromann (2014)[@167636]	Retrospective Questionnaire, mean follow-up 22 years/ 212 HS patients	Long-term prognosis and clinical course of HS based on risk factors	Not applicable	92.2% of HS patients smoked tobacco. 40% (35/88) nonsmokers reported remission vs. 29% (17/59) active smokers reported remission	Small sample size Self-reported information
Liakou (2021)[@167674]	Cross-sectional study/ 290 HS patients	Assess association between active smoking and HS as well as smoking and HS disease severity	Hurley Staging IHS4 score system	Active smoking statistically significant risk factor for higher stage of disease (OR 1.38, 95% CI: 1.11-1.65)	Small sample size Cross-sectional design
Macklis (2021)[@167676]	Cross-sectional online survey/ 591 patients with HS	Determine lifestyle modifications that are associated with HS improvement	Hurley staging	Tobacco cessation showed improvement of HS in 17% of patients. The most significant improvement in subjective and Hurley staging of HS was seen with smoking cessation.	Recall bias Selection bias
Omine (2020)[@167672]	Retrospective case series/ 58 HS patients	Assess the factors associated with HS severity and to compare characteristics of HS patients in East Asia and Western countries	Modified Sartorius Score	Smokers had a Sartorius Score of 48 compared to 57 in never smokers (p = 0.53). Ex-smokers had a Sartorius Score of 38 compared to 57 in never smokers (p = 0.35)	Self-reported information on age of disease onset and comorbidities Fewer mild cases because site is a referral site for severe cases
Revuz (2008)[@167687]	Two case-control studies/ 67 self-reported HS patients, 200 control 302 medically-assessed HS patients and 900 control	Prevalence of HS in French population and associated factors	Not applicable	Strong association with current smoking in self-reported (OR = 4.16, 95% 95 % CI: 2.99-8.69) and in medically assessed (OR = 12.55, 95% CI: 8.58-18.38) populations	Self-reported diagnoses Study design
Sartorius (2009)[@167675]	Cross-sectional/ 251 HS patients	Hidradenitis Suppurativa Score (HSS), BMI, and smoking habits on disease severity	Hidradenitis Suppurativa Score	Median HSS for smokers was 41, former smokers 27, and nonsmokers 22	Cross-sectional design Small sample size
Schrader (2014)[@167639]	Retrospective review/ 864 HS patients	Disease-related factors associated with HS	Hurley Staging	HS severity was associated with smoking pack-years (OR 1.02; p = 0.001)	Self-reported data
Simonart (2010)[@167681]	Case series/ 2 HS patients	Improvement HS lesions with tobacco cessation	Not applicable	24-year-old woman with smoking history, HS refractory to antibiotics and zinc gluconate. Lesions improved 2 months after smoking cessation, no abscess/nodule recurrence 37-year-old woman with smoking history and HS refractory to antibiotics, isotretinoin, and zinc gluconate. HS lesions improved 3 months after tobacco cessation, in remission	Small sample size No controls
Tzellos (2015)[@167670]	Meta-analysis/ Active smoking: 3,997 HS patients, 432 controls History of smoking: 2,472 HS patients, 732 controls	Cardiovascular disease risk factors in HS patients	Not applicable	HS significantly correlated with active smoking (OR 4.34, 95% CI 2.48–7.60, p < 0.001) and history of smoking (OR 6·34, 95% CI 2.41–16.68, p < 0.001)	Meta-analysis of observational studies
Substance Use
Garg (2018)[@167683]	Cross-sectional review/ 32,625 HS patients	Assess the prevalence of substance use disorder (SUD) in patients with HS	Not applicable	Compared to patients without HS, SUD was significantly more prevalent in patients with HS. Prevalence of SUD in HS was 4.0% compared to 2.0% in non-HS patients. Alcohol comprised 47.9% of SUD cases, opioids 32.7% of cases, and cannabis 29.7%. HS patients had an increased chance of 50% of having SUD compared to non-HS patients (95% CI 1.42-1.59; p < 0.001).	SUD could not be accurately diagnosed Cross-sectional design
Lesort (2019)[@167684]	Prospective case-control study/ 641 patients (503 HS patients and 138 psoriasis patients)	Assess prevalence and justifications for using cannabis	Not applicable	Prevalence of cannabis use in HS patients= 34% vs. prevalence in psoriasis patients= 11.6% (p < 0.001) After multivariate analysis, HS patients were 185% more likely to use cannabis than psoriasis patients (OR = 2.85; 95% CI 1.51- 5.64). Close to 69% of patients in the cohort of HS patients started using cannabis before disease onset.	Study design
Patel (2019)[@167685]	Cross-sectional review/ 24,666 HS patients	Measure mental disorders and cost burden associated with HS	Not applicable	The prevalence of mental health disorders was 34.27% for inpatients with HS vs. 20.05% for patients without HS. HS was associated with significantly higher odds of mental health disorder (OR 2.53, 95% CI 2.42-2.63)	Generalizability due to hospitalized patients Potential for missing data
Shlyankevich (2014)[@167686]	Retrospective case-control study/1,730 HS patients and 1,730 controls	Measure the prevalence and comorbidities of HS	Not applicable	Having a drug dependence was associated with higher odds of having HS in univariate analysis (OR 17.2, 95% CI 7.99-37.1) but this association was lost with multivariate analysis. Alcohol dependence was associated with higher odds of having HS compared to controls in multivariate analysis (OR 0.25, 95% CI 0.087 - 0.73)	Ascertainment bias for detecting comorbidities Limited generalizability due to study sample belonging to one academic facility
Revuz (2008)[@167687]	Cross-sectional case-control study/ 67 HS subjects and 200 controls	Describe the prevalence of HS and associated factors	Not applicable	Univariate analysis did not show an association between HS and alcohol consumption or drug use.	Causal relationship not established due to nature of study design
Theut (2018)[@167688]	Cross-sectional questionnaire of Danish blood donors/ 500 HS patients	Estimate prevalence and characterize patients with HS	Not applicable	There was a significant difference in wine and spirit consumption among respondents with HS. Blood donors with HS drank wine significantly less frequently than blood donors without HS (p = 0.02) but spirits/liqueur significantly more frequently (p < 0.001).	Limited external validity
Phan (2020)[@167689]	Meta-analysis/ 62,248 cases and 96,615,486 controls	Perform a meta-analysis to assess the association between HS and substance abuse	Not applicable	HS patients had significantly higher odds of having a substance use disorder (OR 2.84, 95% CI: 2.33–3.46, p < 0.00001), and alcohol abuse (OR 1.94, 95% CI: 1.43–2.64, p < 0.0001).	Significant study heterogeneity
Wehner (2020)[@167690]	Cross-sectional study using an electronic health record database/8,539 HS patients	Characterize the medications prescribed for HS patients	Not applicable	18.1% of patients received an opiate prescription during an HS encounter as compared with 8.5% of psoriasis patients (p < 0.001).	Cross-sectional design HS diagnosis not validated from the dataset