Evaluating the effectiveness of hair-growth products and cosmetics on a broad scale heavily relies on subjective assessments and individual satisfaction. Particularly in cases where the benefits are primarily cosmetic, acknowledging the significant influence of the placebo effect and potential biases is crucial. Therefore, prior to these products reaching consumers, rigorous safety and efficacy testing must adhere to scientific principles, ethical standards, and the rules of good clinical practice and medical research. To be considered valuable, an evaluation method should furnish data on key variables such as hair density (measured as the number of hairs per unit area), linear hair growth rate (LHGR) in millimeters per day, percentage of anagen growth phase (%A), hair diameter in micrometers, and the duration required for hair regrowth after the telogen phase. However, many evaluation techniques lack detailed methodology descriptions and information regarding sensitivity and reproducibility, essential components of clinical investigative techniques. Efforts toward standardizing evaluation methods are crucial to facilitate comparisons across different methods or results obtained from various centers using the same method. These methods can be classified for ease of understanding as invasive, semi-invasive, and non-invasive.

Invasive Methods:


Apart from the conventional vertical sectioning of skin biopsies, which enables the examination of longitudinal follicular sections, horizontal sectioning (parallel to the skin surface) of scalp biopsies presents additional diagnostic possibilities. Initially introduced by Headington, it has been demonstrated that horizontal sectioning may yield superior diagnostic insights compared to vertical sectioning. This technique allows for the examination of a larger number of follicular structures. Inflammatory infiltrates are more readily discernible, and their correlation with follicular structures becomes more apparent than with vertical sectioning. Moreover, fibrous tracts, often challenging to visualize in vertical sectioning, become more evident with horizontal sectioning. Additionally, it facilitates the differentiation between vellus and terminal hairs, enables the identification of various stages of hair growth in a single section, and facilitates the classification of follicles into anagen, telogen, or catagen stages.

Semi-Invasive Methods:


The concept of assessing hair growth changes by examining hair roots was pioneered by Van Scott et al. In order to accurately diagnose hair disorders, it is imperative to examine the status of hair roots, necessitating the plucking of at least 50 hairs to mitigate sampling errors. Subsequently, these roots are scrutinized under a low-power microscope. The stability of root morphology allows for the preservation of hairs in dry packaging for several weeks before analysis. However, due to the generation of relative values such as the telogen/anagen (T/A) ratio, this technique is considered a suboptimal indicator of disease activity and severity, particularly in androgen-dependent alopecia in women. Consequently, in our center, we have ceased utilizing this method due to its reliance on relative values, contrasting with the more robust method detailed in the subsequent section.

Unit Area Trichogram (UAT)

UAT is a method wherein all the hairs within a specified area, typically 60 mm², are plucked and affixed onto double-sided tape on a glass slide. Using optical microscopy, various hair parameters such as hair density, anagen percentage, hair length, and hair diameter are estimated. Before sampling, the scalp area is degreased with an acetone/isopropanol mixture and marked with a roller pen. Each hair within the delineated area is plucked individually, ensuring a uniform grasp above the scalp and rapid, single-action epilation in the direction of hair growth to minimize root trauma.

Interestingly, UAT stands as an exception to a common trend in trichology where methods are often introduced alongside new drugs or cosmetic efficacy evaluation programs. Unlike these methods, UAT has been independently evaluated for reproducibility and clinical relevance, making it suitable for comparative purposes. Most hair growth parameters estimated through UAT and phototrichogram are similar, but UAT holds an advantage as it can be reliably used even in individuals with minimal contrast between hair and skin color.

Noninvasive Methods

Global Methods

Scoring Classification Systems

Hamilton initially described the progressive patterns of scalp hair loss in male pattern baldness in 1951. Subsequently, in 1975, Norwood proposed a modification to Hamilton’s classification, including three patterns relevant to women. In 1977, Ludwig delineated the stages of female androgenetic alopecia, identifying three distinct patterns.


Global Photography Global photography captures all aspects of hairiness simultaneously and is suitable for evaluating the efficacy of drugs, provided that scalp preparation and hairstyle are adequately maintained throughout the study. It’s the most patient-friendly photographic method, commonly employed in clinics under standardized exposure conditions. Processing and rating must occur under controlled conditions, such as being blinded to treatment and/or time, to ensure reproducible data. Trained raters can reliably generate data using this method.

Daily Collection of Shed Hair

The natural cycle of hair growth involves a daily shedding process, where telogen hairs are shed to make way for new anagen hairs. On average, individuals without hair or scalp disorders shed between 40 to 180 hairs per day. In a study involving 404 females without hair or scalp issues, researchers collected shed hair daily over six weeks to compare the effects of two shampoos. The results indicated mean hair loss rates ranging from 28 to 35 hairs per day. Notably, there were no significant differences observed in the mean daily hair loss rates between the two-week baseline period and the subsequent four-week treatment period.In another study involving 234 women who reported hair loss, 89 had what appeared to be normal hair density. The study found that individuals with seemingly normal hair density but experiencing hair loss shed less than 50 hairs per day. This challenges the commonly referenced “magic number” of 100 hairs per day often mentioned in textbooks and the media. Shedding fewer than 50 hairs per day may be considered abnormal, especially in individuals who have already lost 50% of their hair.

Hair Weight and Hair Count

To assess the effectiveness of hair-growth–promoting treatments, researchers can compare the total hair mass (weight) and counts of grown hair within a small, meticulously maintained area of the scalp. A plastic sheet with a 1 cm2 hole is positioned over the designated site. All hairs within this area are pulled through the hole and trimmed by hand to a length of 1 mm. This method offers the advantage of providing a comprehensive measurement of growth using a small sample size, facilitating the detection of drug effects and comparisons between treatment regimens (e.g., 2% vs. 5% minoxidil). However, technical proficiency is crucial to handle samples properly and prevent hair loss between the clinic and the laboratory. Like many techniques, this method lacks methodological comparisons and evaluations of reproducibility and sensitivity typically required for laboratory assessments, as it was primarily introduced for drug evaluation purposes. The main drawback is that it yields a global growth index, and individual components cannot be analyzed separately.

Hair Pull Test

The hair-pull test relies on the notion that gently pulling the hair induces the shedding of telogen hairs. However, it is a coarse method that shows challenging to standardize due to significant interindividual variation among investigators. From a physical standpoint, the pulling force is unevenly distributed across the hair bundle, resulting in variability in the force applied to each hair. Consequently, it appears to be beneficial primarily in acute and severe conditions rather than in chronically evolving conditions such as androgen-dependent alopecia.

Analytical Methods:


The phototrichogram (PTG) involves taking photographs of a scalp area where the hair is cut for better visualization, then repeating this process after a set period to assess hair growth. The method allows for evaluating hair density, anagen percentage, and calculating the rate of hair growth. Despite its noninvasive and patient-friendly nature, some patients may be hesitant due to hair cutting. However, PTG permits chronological follow-up of the same area, providing valuable information over time. Technical improvements, such as frontal window application, have enhanced clarity. Challenges include factors affecting hair visibility in photographs, technician experience, and technical photography issues. Scalp immersion proxigraphy (SIP) has been developed for improved light diffusion. Combining PTG with hair-micrometry offers a valid method for assessing global hair perception and analytical description of hair quality variables.

Variants of Phototrichogram

Video PTG:

In the Video Phototrichogram (PTG) technique, a video camera with specialized lenses replaces the traditional photographic camera. This method has been predominantly reported in studies involving Asian subjects, as the contrast between hair and scalp appears to be advantageous for this approach. Additionally, the observed lower hair density figures may potentially have racial origins. It is advisable to consider these factors to minimize biological variation. The recent availability of inexpensive CCD cameras is expected to drive advancements in this area.

Traction PTG

This test relies on the observation that hairs easily pulled from the scalp are in the telogen phase, while those resisting pull are in the anagen phase. It involves performing the test on a small surface area of 0.25 cm2. Hairs within this area are gently grasped between the thumb and index fingers and pulled repeatedly. The number of hairs easily pulled is counted as telogen hairs, while those resisting pull are clipped and counted as anagen hairs. This method allows for calculating hair density per unit area and anagen percentage.

However, it’s crucial to critically evaluate this semi-invasive method and standardize the pulling technique to ensure reproducibility. Comparative studies are necessary to determine the sensitivity and specificity of this method, which currently has several limitations such as its small surface area and lack of control over traction forces


Neste, G. S. (2001). Hair. In M. P. Andre O. Barel, Handbook of Cosmetic Science and Technology (pp. 40-45). New York: Marcel Dekker, Inc.