One of the best starting points for understanding hair shedding is understanding the hair cycle. A hair strand does not remain in the same biological state continuously; each hair follicle passes through periods of growth, regression, rest and shedding. Scalp hair follicles also cycle independently rather than all moving through these stages at the same time.
The number of hairs shed in a day can vary with the individual, washing frequency, hair length and the way shedding is measured. For that reason, a single rule such as “exactly 50–100 hairs a day is normal and anything above that means disease” should not be used as a diagnostic threshold. A clear increase compared with a person’s usual pattern, visible thinning, the distribution of hair loss and accompanying findings are more informative.
What Is a Hair Follicle?
The hair follicle is described as a dynamic mini-organ capable of repeated regeneration throughout life. Different cellular compartments—including the dermal papilla, hair matrix, inner and outer root sheaths and stem-cell niche—work together. The follicle is also part of the pilosebaceous unit together with the sebaceous gland and arrector pili muscle, and it interacts with the surrounding vascular and neural networks.
During active hair-shaft production, matrix keratinocytes in particular proliferate rapidly. The dermal papilla acts as an important mesenchymal signaling center that communicates with the hair matrix and contributes to regulation of follicle behavior. It is therefore inaccurate to simplify hair production as “dermal papilla cells continuously divide to make the hair shaft.”
Does the Hair Cycle Have 3 Phases or 4?
Classically, the hair cycle is described through three main biological phases: anagen, catagen and telogen. In current literature, however, exogen—the period in which the hair shaft is released and shed from the follicle—is often considered separately.
- Anagen: active growth and hair-shaft production.
- Catagen: a short, controlled regression/transition phase.
- Telogen: a phase in which the follicle is relatively quiescent.
- Exogen: the period in which the telogen club hair is released from the follicle and shed.
That is why some sources describe “three phases” while other contemporary reviews discuss “four phases.” The difference largely reflects whether exogen is separated from telogen.
Anagen: The Active Growth Phase
Anagen is the longest phase and the period in which the hair shaft is actively produced. During anagen, keratinocytes in the hair matrix proliferate intensively, differentiate and keratinize to form the new hair shaft.
For scalp hair, anagen duration is measured in years, but it varies substantially with genetics, age, body site and individual biology. The length of anagen is one of the factors that influences how long a hair strand can become.
Although classic sources state that most scalp hairs are in anagen, phase percentages are not precise universal constants. Measurement method, sampling and the population examined can affect the result. A 2024 study specifically highlighted methodological limitations in the long-established percentages used for catagen and telogen.
Catagen: The Controlled Regression Phase
Catagen is the short regression phase between anagen and telogen. Cellular proliferation decreases, the lower follicle regresses in a controlled manner and follicular architecture is reorganized.
Describing this phase as the follicle “completely detaching from the dermal papilla” or as its “blood supply being cut off” is overly simplistic. The hair cycle is an active remodeling process governed by many interacting local cellular and molecular signals.
Telogen: The Resting Phase
Telogen is the period in which the follicle is relatively quiescent. In scalp follicles this phase is generally measured in months, although duration can vary between individuals and clinical situations.
Telogen should not be treated as exactly the same event as physical hair shedding. A telogen club hair can remain retained in the follicle for a period. The event in which the hair is released and shed is often described separately in current literature as exogen.
Exogen: The Hair-Shedding Phase
Exogen is characterized by reduced retention of the telogen club hair and release of the shaft from the follicle. Exogen can overlap in time with the later part of telogen or with the beginning of a new anagen phase.
This distinction matters because “a shed hair = follicle damage” is not correct. Release of a hair shaft can be part of the normal cycle. In contrast, a marked and persistent increase from a person’s usual shedding pattern, visible thinning or hair loss in specific areas may warrant evaluation for other causes.
What Percentage of Hair Is in Each Phase?
For many years, scalp hair has often been described as approximately 85–90% anagen, 10–15% telogen and 1–2% catagen. These figures can provide a practical general framework, but current research indicates that they should not be treated as fixed biological constants.
Different methods—including hair sampling, phototrichogram and histology—do not necessarily distinguish catagen and telogen with the same accuracy. Hair shedding therefore should not be assessed from phase percentages alone.
What Is Telogen Effluvium?
Telogen effluvium (TE) is a common, usually non-scarring pattern of diffuse hair shedding associated with a greater-than-usual number of follicles shifting from anagen growth toward telogen.
A delay between a triggering event and visible shedding is typical. After a trigger such as febrile illness, major surgery, the postpartum period, substantial physiological stress, rapid weight loss or certain medications, increased shedding may often become noticeable around 2–4 months later.
Acute TE can improve over time in many people when the trigger resolves, but not every case of diffuse shedding should be self-labeled “telogen effluvium.” Chronic TE, androgenetic alopecia, alopecia areata and other causes may need to be considered in the differential diagnosis. Pronounced, persistent or unexplained shedding warrants dermatological evaluation.
What Can Influence the Hair Cycle?
Genetic and hormonal factors: Genetic susceptibility and androgen signaling are important in some hair-loss disorders. Androgenetic alopecia, for example, is a medical hair-loss condition and should not be equated with the action of a cosmetic ingredient.
Illness and physiological stress: Febrile illness, surgery, postpartum hormonal changes, rapid weight loss and some medications can influence transitions between hair-cycle phases.
Nutritional status: Iron stores, protein intake and several micronutrients have been studied in relation to hair health. It is not accurate, however, to assume that every case of shedding means deficiency of iron, zinc, vitamin D or biotin. Testing and supplementation should be guided by history and clinical evaluation.
Scalp disease: Pronounced redness, pain, intense itching, crusting or scarring can indicate a problem that goes beyond routine cosmetic scalp care.
Stress: Physiological and psychological stress are discussed as potential triggers in the telogen-effluvium literature. The process should not be reduced to a single simplistic mechanism such as “cortisol switches the follicle off.”
Does Zinc PCA Change the Hair Cycle or DHT?
For Zinc PCA, which is used in Mirissa Lab products, the core product-communication role is to support the appearance of balanced sebum/oil and scalp care.
Without appropriate finished-product and clinical evidence, it is not appropriate to claim that Zinc PCA “clinically inhibits scalp 5-alpha-reductase, reduces DHT and extends the anagen phase.” The relationship between DHT and androgenetic alopecia is a medical topic and should not be blurred with cosmetic formulation claims.
Does Niacinamide Extend the Hair Cycle?
The strongest cosmetic evidence for Niacinamide relates to epidermal barrier lipids, moisture loss and sebum-focused care. Current evidence does not establish Niacinamide as a direct hair-growth stimulant or as an ingredient that extends anagen.
For that reason, in Mirissa Lab Night Repair Hair Serum we position Niacinamide as barrier-focused care that supports a moisturized, balanced and cared-for scalp appearance.
Do Peptides Start the Anagen Phase?
Mirissa Lab Night Repair Hair Serum contains peptides such as Biotinoyl Tripeptide-1 and Acetyl Tetrapeptide-3. Without appropriate clinical evidence on the finished Mirissa Lab product, however, it is not appropriate to state that these peptides “activate follicle stem cells,” “increase growth factors,” “initiate anagen” or “extend the hair cycle.”
A more defensible cosmetic framework is a multi-peptide approach supporting scalp care and a stronger, fuller and cared-for appearance in hair prone to shedding.
Where Does Cosmetic Care Fit into the Hair Cycle?
A cosmetic product can cleanse the scalp, support moisture and comfort or help hair look stronger and fuller. That does not mean it treats androgenetic alopecia, telogen effluvium or another hair-loss disorder.
In the Mirissa Lab approach:
- Scalp Care Shampoo focuses on cleansing excess sebum and buildup while supporting the appearance of balanced oil with Zinc PCA and a comfortable, cared-for scalp feel with ingredients such as Panthenol, Betaine, Bisabolol and Aloe Vera.
- Night Repair Hair Serum brings together Niacinamide, Zinc PCA, Panthenol, Squalane and peptide complexes across different layers of a scalp-care routine.
These products should be considered a scalp-focused cosmetic care routine, not a medical treatment that changes the hair cycle.
Explore Mirissa Lab Night Repair Hair Serum →
Can the Anagen Phase Be Extended?
Medical treatments targeted to diagnosed hair-loss disorders can influence hair-cycle biology in specific conditions. This does not mean that any cosmetic serum or single cosmetic ingredient can be assumed to extend anagen.
The goal of cosmetic care is to cleanse the scalp appropriately, support moisture and comfort and contribute to a more cared-for hair appearance. When hair loss is pronounced, identifying the cause should come first.
When Should Hair Shedding Be Evaluated by a Dermatologist?
The pattern and change in shedding are often more meaningful than a single daily hair count. Dermatological evaluation is particularly appropriate with:
- sudden or rapidly increasing pronounced shedding,
- visible thinning or widening of the part line,
- patchy/localized hair loss,
- scalp pain, marked redness, heavy crusting or a scar-like appearance,
- associated loss of eyebrow, eyelash or body hair,
- persistent or unexplained diffuse shedding.
Laboratory testing should also be guided by history, examination and suspected causes rather than applying the same universal panel to everyone.
Frequently Asked Questions
How many phases does the hair cycle have?
Classically, three main phases are described: anagen, catagen and telogen. In current literature, exogen—the period when the hair shaft is released from the follicle and shed—is often separated as a fourth phase.
Does a telogen hair always shed immediately?
No. A telogen club hair can remain retained in the follicle for a period. Physical release and shedding can occur during exogen.
Does shedding more than 100 hairs a day automatically mean disease?
No. A daily hair count is not diagnostic by itself and is affected by washing and measurement methods. A clear change from the person’s usual pattern, visible thinning and the distribution of hair loss are more important.
When does telogen effluvium appear?
Visible diffuse shedding may often appear around 2–4 months after a trigger. Not every case of diffuse shedding, however, is telogen effluvium.
Does Mirissa Lab serum extend the anagen phase?
We do not make this claim without appropriate clinical evidence on the finished product. The serum is positioned for scalp care and to support a stronger, fuller and cared-for appearance in hair prone to shedding.
Which blood tests are needed for hair shedding?
There is no single universal panel. Testing should be based on medical history, nutritional context, accompanying symptoms and dermatological evaluation.
Scientific References
- Integrative and Mechanistic Approach to the Hair Growth Cycle and Hair Loss. J Clin Med. 2023. PMID: 36769541.
- The Proportion of Catagen and Telogen Hair Follicles in Occipital Scalp of Male Androgenetic Alopecia Patients: Challenging the Established Dogma. Exp Dermatol. 2024. PMID: 39422326.
- Exogen hair characterization in human scalp. Skin Res Technol. 2007. PMID: 17908196.
- Telogen Effluvium: A Review. J Clin Diagn Res. 2015. PMID: 26500992.
- Hair Shedding Evaluation for Alopecia: A Refined Wash Test. Clin Cosmet Investig Dermatol. 2022. PMID: 35115799.
This content is for informational purposes only and does not constitute medical advice. Mirissa Lab products are cosmetic care products.
