10.5826/dpc.1304a237
Androgenetic alopecia (AGA) is a common hair loss condition that impacts both men and women. Age and genetic susceptibility are recognized as potential risk factors for developing AGA. The second to fourth digit ratio is a measurement of the length ratios between the index and ring fingers. This ratio has been utilized as a predictor for multiple hyperandrogenism-related medical conditions. More recently, the 2D:4D ratio was investigated as a predictor for AGA. This article will examine the evidence supporting this relationship, discuss its diagnostic implications, and identify potential areas for future research.
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text/xml
2160-9381
3345
en
Asem Shadid
https://creativecommons.org/licenses/by-nc/4.0
Dermatology Practical & Conceptual
review
The Use of 2D: 4D Digit Ratio as a Predictor of Androgenetic Alopecia: A Review
Text.Serial.Journal
https://dpcj.org/index.php/dpc
Review
2023-10-31
2023-03-15
2023-10-31
2024-01-15
Dermatol Pract Concept
Androgenetic alopecia (AGA) is a common hair loss condition that impacts both men and women. Age and genetic susceptibility are recognized as potential risk factors for developing AGA. The second to fourth digit ratio is a measurement of the length ratios between the index and ring fingers. This ratio has been utilized as a predictor for multiple hyperandrogenism-related medical conditions. More recently, the 2D:4D ratio was investigated as a predictor for AGA. This article will examine the evidence supporting this relationship, discuss its diagnostic implications, and identify potential areas for future research.
&nbsp;
Asem Shadid
2023/10/31
10.5826/dpc.1304a237
Department of Dermatology, King Fahad Medical City, Riyadh, Saudi Arabia
2160-9381
review
en
Bilgic Ö, Altınyazar HC, Eryılmaz D, Tuğrul ZA. Are 2D:4D finger-length ratios an indicator of androgenetic alopecia in males? An Bras Dermatol. 2016 Apr;91(2):156–9.
The Use of 2D: 4D Digit Ratio as a Predictor of Androgenetic Alopecia: A Review
https://dpcj.org/index.php/dpc/article/download/3345/2351
           The Use of 2D:4D Digit Ratio as a Predictor
              of Androgenetic Alopecia: A Review
                            Mohammed Almashali1, Khalid Alekrish2, Asem Shadid3


1 Department of Dermatology, College of Medicine, Imam Mohammad Ibn Saud Islamic University, Riyadh, Saudi Arabia
2 Department of Dermatology, College of Medicine, King Saud University, Riyadh, Saudi Arabia
3 Department of Dermatology, King Fahad Medical City, Riyadh, Saudi Arabia



Key words: digits, 2D:4D, androgenic alopecia, hair loss, review
Citation: Almashali M, Alekrish K, Shadid A. The Use of 2D: 4D Digit Ratio as a Predictor of Androgenetic Alopecia: A Review.
Dermatol Pract Concept. 2023;13(4):e2023237. DOI: https://doi.org/10.5826/dpc.1304a237
Accepted: April 13, 2023; Published: October 2023
Copyright: ©2023 Almashali et al. This is an open-access article distributed under the terms of the Creative Commons
Attribution-NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted
noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited.
Funding: None.
Competing Interests: None.
Authorship: All authors have contributed significantly to this publication.
Corresponding Author: Khalid Alekrish, Department of Dermatology, College of Medicine, King Saud University, PO Box 56810,
Riyadh 11564, Saudi Arabia. E-mail: khalidalekrish@gmail.com.




  ABSTRACT             Androgenetic alopecia (AGA) is a widespread type of hair loss that affects both males and females.
                       Advanced age and family history of AGA are well-established risk factors for developing AGA. The
                       second to fourth digit ratio (2D:4D) is the ratio between the length of the index and ring fingers. This
                       ratio has been utilized as a predictor for multiple hyperandrogenism-related medical conditions. More
                       recently, 2D:4D was investigated as a predictor for AGA. This article aims to investigate the evidence
                       supporting the use of 2D:4D as a predictor of AGA, and address areas of future research.




Introduction                                                                  Furthermore, androgenetic alopecia can have many
                                                                         psychological repercussions including low self-esteem, low
Androgenetic alopecia (AGA) is a prevalent type of hair loss             mood, anxiety, and social withdrawal [6,7]. Moreover, ad-
affecting both males and females. It impacts roughly eighty              vanced age and genetic susceptibility, including family history
percent and fifty percent of males and females, respectively             of AGA are all well-recognized risk factors for AGA [8,9].
[1,2]. Androgens shorten the anagen phase of the hair folli-                  A recently emerging indicator for the identification of
cle, which, in turn, leads to a reduction in its size and minia-         different medical conditions is the second-to-fourth digit ra-
turization of the hair—the hallmark of AGA [3-5].                        tio, also known as the 2D:4D. The second to fourth digit




Review | Dermatol Pract Concept. 2023;13(4):e2023237                                                                                  1
ratio (2D:4D) is the ratio between the length of the index             of four articles were identified that specifically examined the
and ring fingers. This ratio has been utilized to predict the          value of the 2D:4D in predicting the risk and severity of an-
risk of hyperandrogenism, high body mass index and waist-              drogenetic alopecia.
to-hip ratio, and benign prostatic hyperplasia [10-12].
      Recent studies have investigated the potential of the
                                                                       Results
2D:4D as a predictive factor for AGA. It is postulated that
a lower 2D:4D ratio may signify elevated levels of perinatal           Few studies have been conducted to specifically assess the
testosterone, thereby serving as an indicator for an increased         association between a low 2D:4D and a higher risk of de-
likelihood of developing AGA [13,14]. This article aims to             veloping AGA (Table 1). The most recent of which was a
investigate the evidence supporting the use of 2D:4D as a              cross-sectional study conducted by Chen et al. in 2022,
predictor of AGA, and address areas of future research.                which included 240 patients with varying degrees of AGA se-
                                                                       verity. The authors found that individuals with a right-hand

Methods                                                                2D:4D less than 0.947 (index finger shorter than ring finger)
                                                                       may have a more severe form of AGA (P = 0.036). Nonethe-
A comprehensive literature search was conducted in the                 less, factoring in patients’ age as a predictor for AGA risk
Medline and Google Scholar databases from their com-                   alongside the 2D:4D was shown to be superior to either pre-
mencement until February 2023. The search combined terms               dictor alone, resulting in an odds ratio of 6.1, as opposed to
related to the second-to-fourth digit ratio (“Second-to-fourth         2.8 when 2D:4D is used by itself [15].
digit ratio OR “2D:4D ratio” OR “Digits”) and androge-                     To this date, a single-center, descriptive, analytical study
netic alopecia (“Androgenetic alopecia” OR “Androgenic                 involving 1200 Iranian men is the largest and most controlled
alopecia” OR “AGA”). There were no language restrictions.              study conducted to assess the association between digit
Additionally, references of included articles and relevant re-         length and AGA risk. The study sample was selected using
views were manually searched for additional studies. A total           random sampling and was stratified based on the severity of



 Table 1. Summary of the studies conducted to assess the association between Second-to-fourth digit
                                  ratio and androgenetic alopecia.
                                                                       Mean patient
     Study        Study design             Sample size (N)            age in years (SD)                      Results
 Chen et al, Cross-sectional         240                             32.9 (8.4)             Significant association between low
 2022 [15] studya                                                                           2D:4D of the right hand and higher
                                                                                            grade of AGA (P = 0.036). Significant
                                                                                            association between older age and a
                                                                                            higher grade of AGA (P = 0.006).
 Unal, 2018 Case-control             189 (Case and control           Case group:            Significant association between low
 [19]       studya                   groups included 99 and 90       29.7 (5.5).            2D:4D of the left hand and having AGA
                                     patients, respectively)b        Control group:         (P < 0.001). No significant relationship
                                                                     19.6 (5).              between 2D:4D and the severity of
                                                                                            AGA in either the left or right hands.
 Bilgic et al, Cross-sectional       360 (Case and control           Not stated.            Significant association between low
 2016 [20] studya                    groups included 189 and                                2D:4D of the right hand and having
                                     171 patients, respectively)b                           AGA (P < 0.001). No significant
                                                                                            relationship between 2D:4D and the
                                                                                            severity of AGA in either the left or
                                                                                            right hands.
 Feily et al,    Single-site,      1200                              33.2 (0.28)            No significant association between low
 2016 [16]       descriptive-                                                               2D:4D of the right (P = 0.747) or left
                 analytical studya                                                          (P = 0.337) hand and having AGA.
                                                                                            Positive correlation coefficient identified
                                                                                            between low 2D:4D and AGA only in
                                                                                            individuals older than 40 years of age.
 AGA = Androgenic alopecia; SD = standard deviation;2D:4D: Second-to-fourth digit ratio.
 a
    Norwood scale was used to assess the severity of AGA. Second- and fourth-digits length was measured using a digital vernier caliper.
 b
    Patients with AGA grades I and II have been excluded from the study.




2                                                                                  Review | Dermatol Pract Concept. 2023;13(4):e2023237
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