Table 3.

Studies showing negative co relation between smoking and hair loss

Author	Place of study	Year of publication	Study design	Patient	Duration of study	Study subject details	Smoking status	Observation and results
Matilainen et al.[32]	Finland	2003	Controlled retrospective trial	n=324 female	Part of cohort study which was started in 1990	Ludwig’s scale. Modification was used to asses hair status. The prevalence of extensive hair loss at least grade II or III on Ludwig’s scale was high (31.2%)	Not included	Both groups of normal hair and extensive hair loss, prevalence of smoking was low and equal (P=0.918)
Severi et al.[33]	Australia	2003	Controlled retrospective trial	n=1390 men	Age stratified, population-based case-control study. Cases who were diagnosed Adenocarcinoma of prostrate before 70 years during 1994-1997 were included	Interviewers scored AGA according to the Hamilton-Norwood scale as described below. No balding n=350 (Hamilton-Norwood stage I), front balding n=447 (Hamilton-Norwood stage II, III, IIIa, and Iva) vertex balding n=238 (Hamilton Norwood stage III-vertex and 5) and frontal AGA with vertex AGA n=335 (Hamilton Norwood stage 4, 5, 5a, 6, and 7)	Defined as either nonsmokers, current smokers, or ex-smokers	Prevalence of frontal only AGA was higher in nonsmokers (199/447) than in current (73/447) and ex-smoker groups (175/447). Vertex only AGA was higher in nonsmokers (106/238) than in current (41/238) and ex-smokers (91/238). Frontal AGA along with vertex AGA was higher in nonsmokers (173/335) than current (47/335) and ex-smokers (135/335) (P>0.05)
Nargis et al.[21]	Manglore	2017	Uncontrolled prospective study	n=103	1.6 years	The questionnaire was based on classification of AGA, age at onset of AGA, duration of hair loss, smoking, and other risk factors	Smoking status classified as never or current and further categorized as <20 cigarette and >20 cigarette	Among 41 smokers, 22 smoked<20 cigarette/day and had AGA before 35 years (P=0.014) Moreover, in group of >20 cigarettes per day, 13 had onset before 35 years and 6 patients had onset after 35 years, statically insignificant
Danesh- shakiba et al.[34]	Iran	2020	Controlled prospective trial	n=512 male	8 months (January 2018-September 2018)	256 patients with AGA and 256 age-matched control subjects were included with mean age of 38.3 and 38.4 years, respectively. The Norwood-Hamilton scale was used to determine the presence and severity of AGA by single physician	Current smokers who smoked cigarette in past 30 days	Smoking was not statistically significant among AGA subjects 72 (28.1%) compared to control subjects 66 (25.8%) (P=0.550). Smoking was not significantly more common in patients with mild-to-moderate hairless
Salman et al.[35]	Turkey	2017	Controlled retrospective trial	n=954 (419 males, 535 females)	8 months (October 2013-May 2014)	Average age of 37.7 years. AGA prevalence found was 67.1% (n=281) in men and 23.9% (n=128) in women. Severity of AGA was evaluated with Norwood-Hamilton scale in men and Ludwig classification in women	Not included	No significant difference was seen between smokers and nonsmokers
Lai et al.[36]	Taiwan	2013	Controlled prospective trial	n=354 male	5 years	Age range was 35-65 years. The Norwood-Hamilton scale was employed to asses severity	Not included	In subjects with Hamilton-Norwood scale score of I-III, 175 (59.5%) subjects were smokers and 119 (40.5%) subjects were nonsmokers. Subjects with a Hamilton- Norwood scale of IV-VII, 35 (58.3%) subjects were smokers and 25 (41.7%) were nonsmokers

AGA – Androgenetic alopecia