Table 2.

Studies showing positive correlation between smoking and hair loss

Author	Place of study	Year of publication	Study design	Sample size	Duration of study	Study subject details	Smoking status	Observation and results
Mosley and Gibbs[22]	United Kingdom	1996	Controlled retrospective trial	n=606 (male=268, female=338)	3 months	Age group>30 years 152 males and 152 females were smokers. Hamilton badness scale. Category III and above regarded as bald. Bald smokers male 103; female 2 Bald nonsmokers male 63, female 2	Not included	Odds ratio for association of smoking and baldness in men was 1.93 (95% confidence interval 1.13-3.28). For females, corresponding calculation was not done
Su and Chen[23]	Taiwan	2007	Uncontrolled retrospective trial	n=740	2 months (April 2005-June 2005)	Mean age 65 years Norwood and Ludwig classification system. In age group 40-49, 50-59, 60-69, and >70, the age specific prevalence of Norwood type A variant were 5.1, 1.1, 8.1, and 7.4%, respectively, and those of female pattern AGA were 0.0, 2.1, 1.6, and 2.4%, respectively	Smoking status categorized as never, quit, current smoker of <20 cigarettes and smokers of >20 cigarette a day	Smokers had an increased risk of moderate or severe AGA (Norwood type 4) and smoking status (OR, 1.77; 95% CI, 1.14-2.76), current cigarette smoking of 20 cigarettes or more per day (OR, 2.34; 95% CI, 1.19-4.59), and smoking intensity (OR, 1.78; 95% CI, 1.03-3.07)
Fortes et al.[24]	Italy	2017	Uncontrolled, retrospective trial	n=351 (237 males, 114 females)	1 year (2010-2011)	Mean age: 35 years Male: 133 subjects with mild (Hamilton-Norwood classifications I-III) and 104 subjects with moderate and severe (Hamilton Norwood classification IV-VII). Female: 104 subjects with mild (Ludwig type 1) and 10 subjects with moderate/severe (Ludwig types II and III)	Subjects categorized as never, quit, current smokers of <10 cigarettes and smokers of >10 cigarette per day	Subjects with severe AGA smoked more as compared to less severe AGA (17.5 versus 7.6%, P=0.05). Furthermore, AGA subjects who were heavy smokers had almost 3 times an increased risk of having a moderate/severe alopecia in comparison to who never smoked
Salem et al.[25]	Egypt	2021	Controlled prospective trial	n=1000 (smokers 500; nonsmokers 500)	1 year 6 months (January 2018-September 2019)	Mean age 25 years of smokers group 235 (47%) had grade 3 AGA and 120 subjects (24%) had grade4 AGA. In the nonsmoker group, 100 subjects (20%) had grade 2 AGA and 50 subjects (10%) had either grade 3 or 4 AGA	Smokers were who smoked >10 cigarette over >1 year	Majority of smokers (425) had a form of AGA while only (200) nonsmokers had a degree of AGA (P<0.01)
Park et al.[26]	Korea	2016	Controlled retrospective trial	n=1884 (male=915, female=969)	2 years (October 2012-December 2014)	Mean age of 56.6 years 991 was AGA patients (613 males, 378 females) of the 991 AGA patients, 443 subjects were classified as having mild AGA, 381 had moderate AGA, and 167 had severe AGA. BASP classification was used to evaluate hair loss	Divided as presence or absence of smoking	Smokers in AGA group 334/991 (33.7%) were higher than the non-AGA group 214/892 (24%) (P=0.0000). Subjects with more smoking had more severe form of AGA [mild: 125/443 (28.2%), moderate: 143/381 (37.5%), severe 66/167 (39.5%) (P=0.004)
Gatherwright et al.[27]	Ohio	2012	Controlled retrospective trial	n=98 female	2 years (2009-2011)	98 female identical twins (49 sets) mean age 53 years	Not included	Frontal hair loss noted less in twins who had never smoked (P=0.021; n=8). Increased frontal hair thinning was also significant in smokers. Temporal hair loss more in smokers (P=0.096, n=10)
Vora et al.[28]	Gujarat, India	2019	Controlled prospective trial	n=100 male	2 years (June 2014-May 2016)	50 subjects with AGA and 50 age-matched control subjects were included with a mean age of 29.32 and 31.5 years, respectively. The degree of androgenic alopecia was based on the Norwood scale (3-7). AGA developing before 36 years of age and reaching at least stage 3 of Hamilton-Norwood classification is termed as early onset AGA	Not included	The prevalence of smoking was higher in male patients with early onset AGA. 26 (52%) as compared to controls 11 (22%) (P=0.002)
Gatherwright et al.[29]	Ohio	2013	Controlled retrospective trial	n=92 male	2 years (2009-2011)	92 male identical twins (46 sets). Mean age 52 years	Not included	Increased smoking duration and frontal hair loss showed positive co relation (P<0.001), but quantity of smoking was not statistically significant. Twins who smoked had more vertex hair loss than their nonsmoking siblings (P=0.047, n=20)

AGA – Androgenetic alopecia; OR – Odds ratio; CI – Confidence interval; BASP – Basic and specific