1. Introduction
Hair growth is a complex process that many factors, including environmental and internal stimuli, can affect by changing the blood supply and metabolism of the hair follicles. These stimuli cause hair growth in a part of the body to be thicker and longer than the standard amount in the same part according to age, gender, or race. Excessive and abnormal growth of body hair occurs in two disorders, hypertrichosis and hirsutism [1]. Hirsutism refers to the abnormal growth of body hair with a male pattern in women and children, which is not investigated in this study.
Hypertrichosis refers to excessive and abnormal growth of vellus hair that occurs for any reason and is independent of the effect of androgens. Hypertrichosis may be localized or diffuse, and acquired or congenital [2]. Acquired locally is one of the typical types of hypertrichosis, which is usually caused by inflammation and skin hyperemia, as a result of infections and trauma [1]or even vaccine injection [3].
Since opening the cast of broken limbs, hypertrichosis has been observed in the mentioned limb, hyperemia and inflammation caused by trauma and fracture or changes in vascularity following bone fixation and surgery is responsible for this acquired local hypertrichosis [1, 4].
This type of hypertrichosis is caused in many cases by the casting of limbs. Although it is reported in a few cases and is less known to general practitioners and dermatologists, it is well-known to surgeons and orthopedic specialists [1, 5].
This type of hypertrichosis is reversible and the thickness and amount of body hair returns to its original state after a period. Also, according to previous studies in this field, a longer duration of body cast leads to more time required to resolve hypertrichosis in the mentioned limb [6].
Since acquired local hypertrichosis occurs unilaterally in the same organ, it causes asymmetry and causes problems in terms of beauty. Accordingly, it is necessary to investigate the prevalence of hypertrichosis after the casting of broken limbs to resolve the concerns of patients in case of occurrence, preventive measures, and timely treatment.

2. Methods
This prospective cohort study was conducted in the orthopedic department of Hazrat Rasul Akram educational, research and treatment complex to investigate hypertrichosis after limb casting for fractures. Sampling was carried out consecutively, and patients who had visited the orthopedic department of Hazrat Rasul Akram educational, research and treatment complex due to limb trauma (without limitation of upper or lower limbs) in 2019 and required casting were evaluated. 
The inclusion criteria were as follows: The absence of localized or generalized hypertrichosis in the patient before entering the study and the need for casting on one of the limbs without trauma or damage in the opposite limb requiring casting. 
The exclusion criteria included the patient’s unwillingness or lack of consent to participate in the study and failure to attend to cast removal appointment.
All patients who met the inclusion criteria were included in the study. Demographic and clinical information, including age, sex, history of surgery on the affected limb, number of casts, and duration of casts were collected through interviews or by referencing the patient’s clinical file and the severity of the trauma and the presence or absence of hypertrichosis was also determined through clinical examination.
The data were then entered into the SPSS software, version 24 for analysis. The results for quantitative variables were expressed as Mean±SD, while categorical qualitative variables were presented as percentages. A relevant statistical test was employed to compare and examine the relationship between various components. Quantitative variable comparisons were performed using the t test. In cases of non-normal distribution, the Mann-Whitney test was employed. Qualitative variable comparisons were conducted using the chi-square test or the Fisher exact test. The significance level for all tests in this study was set at 0.05, with a confidence interval of 95%. 
This study was conducted following the principles of medical ethics. Before commencing the study, informed consent was obtained from all patients. The names of the participants were not disclosed, no interventions were performed, and no additional costs were imposed on the participants.

3. Results
Demographic and clinical data of all patients are provided in Table 1.

The mean age in the two study groups was significantly different from each other in terms of hypertrichosis status (P=0.0001). Patients with hypertrichosis were significantly younger than patients without hypertrichosis. No significant relationship or difference was found regarding other variables (P>0.05) (Table 2).



4. Discussion
There have been few studies with a large number of patients on this subject, although a few cases of post-cast hypertrichosis have been reported [8, 9, 10].
Out of the 82 participants in this study, only 7 patients exhibited hypertrichosis after casting (8.5%). In contrast, Akoglu et al. (2012) reported a rate of 34.2% [7]. The mean age of all patients in this study was 41 years, whereas the mean age of the 7 individuals with hypertrichosis was 10.57±4.75 years. Notably, all patients with hypertrichosis belonged to the children and adolescents age group. Furthermore, a significant difference in the mean age of the two groups was observed (P=0.0001), which is in line with the findings of Akoglu et al. [7].
Gender distribution was balanced in our study, with an equal number of men and women, thus mitigating gender-related biases.
Among the 7 patients with hypertrichosis, 6(85.7%) were women, whereas the gender distribution among the 75 patients without hypertrichosis was nearly equal and close to each other. The comparison revealed no significant difference between the two groups in terms of gender (P=0.109).
The mean casting duration was approximately 4.6 weeks, equivalent to about 32 days. The group with hypertrichosis had a mean casting duration of about 3 days longer than the group without hypertrichosis, even though this difference lacked statistical significance (P=0.307). Notably, Agoklu et al. also did not observe any significant difference in this regard [7]. According to a study conducted by Chairerg  et al. (2014) on 14 patients, cast application for 4 weeks can significantly stimulate hair growth [11].
Regarding the frequency of casting, only two of the 82 patients participating in the study had been plastered twice, and both of them belonged to the group without hypertrichosis. All individuals with hypertrichosis had been plastered only once, indicating no significant difference between the two groups in this regard (P=1.000). This result is in line with the findings of the study by Agoklu et al. [7].
The frequency of history of surgery on the affected limb was slightly different between the two groups. In the group with hypertrichosis, the number of people with no history of surgery was equal to the number of people who had undergone surgery once. In contrast, in the group without hypertrichosis, the number of people without a history of surgery was more than twice the number of individuals who had a history of surgery only once.
Regarding the condition and severity of the trauma, the highest frequency in the group without hypertrichosis was related to minor fractures, accounting for 53.3%. In the group with hypertrichosis, the number of individuals with minor fractures and those with high-energy fractures was equal. No significant difference was observed between the two groups in this aspect (P=0.360).
The location of injury in individuals with hypertrichosis had different distributions; however, 6 out of 7 individuals had injuries in the upper limbs. In the group without hypertrichosis, this matter was slightly different, with the percentage of upper limb injuries being almost equal to the lower limb injuries.

5. Conclusion
The incidence of hypertrichosis in Iranian society is slightly lower than in other societies, standing at 8.5%. Younger patients in Iran are more susceptible to developing hypertrichosis after limb casting for fractures.

Study limitations
One of the limitations of this study, when compared to previous studies, is the absence of long-term follow-up of the patients to determine the mean time for hypertrichosis resolution. Additionally, measurements of indicators, such as hair length, diameter, and density after casting were not conducted. Therefore, it is recommended that future studies with a larger sample size, longitudinal design, and longer follow-up duration be conducted to address these aspects.

Ethical Considerations
Compliance with ethical guidelines
The study was approved by the Ethical Committee of the Iran University of Medical Sciences (Code: IR.IUMS.FMD.REC.1398.350).

Funding
his research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
Study design: Ali Yeganeh; Supervision and Writing the original draft: Amir Ebrahimzadeh Babaki; Data collection and data analysis: Anahid Bagheripour; Final approving: All authors.

Conflict of interest
The authors declared no conflicts of interest.


References

1. Ma HJ, Yang Y, Ma HY, Jia CY, Li TH. Acquired localized hypertrichosis induced by internal fixation and plaster cast application. Ann Dermatol. 2013; 25(3):365-7. [DOI:10.5021/ad.2013.25.3.365] [PMID] 
2. Wendelin DS, Pope DN, Mallory SB. Hypertrichosis. J Am Acad Dermatol. 2003; 48(2):161-79; quiz 80-1. [DOI:10.1067/mjd.2003.100] [PMID]
3. Manchanda K, Mohanty S. Localized hypertrichosis following vaccination in an infant. Int J Trichology. 2016; 8(2):84-6. [DOI:10.4103/0974-7753.188037] [PMID] 
4. Leung AK, Kiefer GN. Localized acquired hypertrichosis associated with fracture and cast application. J Natl Med Assoc. 1989; 81(1):65-7. [PMID]
5. Rathi SK. Localized acquired hypertrichosis following cast application.Indian J Dermatol Venereol Leprol. 2007; 73(5):367. [Link]
6. Pfiester MP, Eismann EA, Wilson LM, Parikh SN. Localized acquired hypertrichosis after cast treatment in pediatric and adolescent patients: A natural history study.  J Pediatr Orthop. 2013; 33(7):755-8. [DOI:10.1097/BPO.0b013e31829e7d3d] [PMID]
7. Akoglu G, Emre S, Metin A, Bozkurt M. High frequency of hypertrichosis after cast application. Dermatology. 2012; 225(1):70-4. [DOI:10.1159/000341521] [PMID]
8. Pick RY. Focal hair growth under the plaster-of-Paris cast. N Y State J Med. 1980; 80(11):1726. [PMID]
9. Chang CH, Cohen PR. Ipsilateral post-cast hypertrichosis and dyshidrotic dermatitis. Arch Phys Med Rehabil. 1995; 76(1):97-100. [DOI:10.1016/S0003-9993(95)80050-6]
10. Kara A, Kanra G, Alanay Y. Localized acquired hypertrichosis following cast application. Pediatr Dermatol. 2001; 18(1):57-9. [DOI:10.1046/j.1525-1470.2001.018001057.x] [PMID]
11. Chairerg P, Tantavisut S, Tanavalee A, Tuangjaruwinai W, Panchaprateep R, Asawanonda P. Cast application of four weeks’ duration significantly affects hair length, diameter and density. J Dermatolog Treat.2014; 25(2):178-81. [DOI:10.3109/09546634.2013.789471] [PMID]