Anagen-Telogen Ratio: What Your Hair Growth Cycle Tells You

In a healthy scalp, 85 to 90% of hairs are in the anagen (growth) phase at any given time. In androgenetic alopecia, that number can drop below 70%, and the resulting shift in your growth cycle is one of the earliest measurable indicators of progressive hair loss. Understanding how this ratio works gives you a framework for interpreting shedding patterns, evaluating treatment response, and distinguishing between temporary setbacks and genuine long-term decline.

The Three Phases of Hair Growth

Every hair on your scalp follows a repeating cycle of growth, transition, and rest. These phases operate independently for each follicle, which is why you shed roughly 50 to 100 hairs per day under normal conditions without noticing any thinning. Problems arise when this staggered cycling breaks down.

Anagen Phase (Active Growth)

The anagen phase is when the hair follicle is actively producing a hair shaft. This is the longest phase and the one that determines how long your hair can grow.

• Duration: 2 to 7 years (genetically determined)
• Hair growth rate: Approximately 1 cm per month (0.35 mm per day)
• Percentage of scalp hairs: 85-90% in healthy individuals
• What happens: The dermal papilla receives blood supply, the matrix cells divide rapidly, and a keratinized hair shaft pushes upward through the follicle

The length of your anagen phase is why some people can grow hair to their waist while others find their hair "stops growing" at shoulder length. The hair is not actually stopping; it is reaching the end of its individual anagen cycle.

Catagen Phase (Transition)

Catagen is a brief transitional period where the follicle begins to shut down active growth.

• Duration: 2 to 3 weeks
• Percentage of scalp hairs: Approximately 1%
• What happens: Blood supply to the dermal papilla is cut off, the lower portion of the follicle collapses, and the hair shaft detaches from the base (forming a "club hair")

Because catagen is so short, it represents a tiny fraction of hairs at any given time. It is clinically important mainly as a marker of the transition from growth to rest.

Telogen Phase (Resting and Shedding)

During telogen, the hair sits dormant in the follicle until it is eventually pushed out by a new anagen hair growing beneath it.

• Duration: 3 to 4 months
• Percentage of scalp hairs: 10-15% in healthy individuals
• What happens: The hair shaft remains anchored loosely in the follicle. It falls out during washing, brushing, or when the new hair pushes it from below.

A fourth phase, exogen (active shedding), is sometimes classified separately. During exogen, the club hair physically separates from the follicle and falls out. This is the hair you see on your pillow, in the shower drain, or on your brush.

How Androgenetic Alopecia Disrupts the Cycle

The core mechanism of pattern hair loss is not that follicles die. Instead, DHT sensitivity causes the anagen phase to shorten progressively with each cycle. Here is what that looks like over time.

Cycle Compression Timeline

This compression explains several phenomena that confuse people tracking their hair loss:

Increased shedding with shorter hairs. As anagen shortens, more follicles cycle through telogen per month. Instead of a follicle producing one hair over 5 years, it might produce multiple shorter hairs in the same period, each of which eventually sheds. This can actually increase your daily hair count on the pillow, even though each individual hair contributes less to visual density.

Seasonal variation. Normal seasonal shedding (higher in late summer and fall) can temporarily shift the anagen-telogen ratio. This is not the same as androgenetic alopecia, but it can mask or exaggerate AGA-related changes in tracking data.

Post-treatment shedding. When starting finasteride or minoxidil, some users experience a temporary increase in shedding during the first 1 to 3 months. This happens because treatment pushes resting telogen hairs into a new anagen cycle, causing the old hairs to shed before the new, healthier hairs emerge.

Measuring the Anagen-Telogen Ratio

Clinical Methods

A trichologist or dermatologist measures the anagen-telogen ratio using one of several techniques:

Trichoscopy (dermatoscopy of the scalp): A dermatoscope at 10x to 70x magnification allows the clinician to visualize hair shafts emerging from follicles. Anagen hairs have a characteristic tapered tip, while telogen hairs show a club-shaped root. The ratio of these provides a direct measurement.

Phototrichogram: A small area of scalp is clipped, photographed, and then photographed again 3 days later. Hairs that have grown (even 1 mm) are in anagen. Hairs that show no growth are in telogen or catagen. This is considered the gold standard for cycle measurement.

Trichogram (hair pluck test): A clinician pulls approximately 60 to 80 hairs from a defined area and examines the roots under a microscope. Anagen roots are elongated and pigmented; telogen roots are rounded and club-shaped. While accurate, this method is uncomfortable and samples a limited area.

What Home Tracking Can Reveal

You cannot measure your anagen-telogen ratio precisely at home. However, consistent photo tracking reveals indirect indicators of cycle disruption:

• Increasing proportion of short hairs in a tracked region suggests anagen shortening
• Changes in density over 3 to 6 months that exceed normal seasonal variation point to a shifted ratio
• A rising count of thin, wispy hairs alongside stable or declining thick hairs indicates miniaturization driven by shortened anagen

These indirect signals are why monthly photo tracking, even without clinical magnification, provides actionable data. For a detailed look at how miniaturization works alongside cycle changes, see our hair miniaturization guide.

Anagen-Telogen Ratio in Different Conditions

The ratio shifts differently depending on the underlying cause of hair loss.

Androgenetic Alopecia (Pattern Baldness)

• Anagen percentage drops gradually over months to years
• The shift is regional (temples and crown first in men, diffuse in women)
• Ratio may be 70 to 80% anagen in affected areas vs. 85 to 90% in unaffected donor zones
• Responds to DHT-blocking treatments (finasteride) and growth stimulants (minoxidil)

Telogen Effluvium

• Anagen percentage can drop sharply to 60 to 70% within weeks
• The shift is diffuse across the entire scalp
• Usually triggered by a specific event (illness, surgery, stress, nutritional deficiency, hormonal change)
• Self-resolving within 3 to 6 months once the trigger is removed
• Daily shedding may spike to 200 to 300+ hairs

Alopecia Areata

• Follicles are attacked by the immune system during anagen, causing premature catagen
• Results in sudden, patchy hair loss (not gradual like AGA)
• Anagen ratio in affected patches drops to near zero
• Surrounding areas may maintain normal ratios

Knowing which condition is affecting your ratio is critical because the treatment approach differs entirely. Tracking data that shows gradual, regional change over months points toward AGA. Sudden, diffuse shedding that started after a specific event suggests telogen effluvium. Patchy, rapid loss may indicate alopecia areata.

How Treatments Affect the Anagen-Telogen Ratio

Finasteride

By reducing DHT levels (blocking approximately 60 to 70% of scalp DHT), finasteride allows affected follicles to maintain longer anagen phases. In clinical studies:

• Anagen-telogen ratios in treated patients improved by 10 to 15 percentage points over 12 months
• The improvement was most pronounced in the vertex (crown) area
• 80 to 90% of men maintained or improved their ratio over 5 years
• Side effects occur in 2 to 4% of users

Minoxidil

Minoxidil (5% topical, applied twice daily) works partly by extending the anagen phase and shortening the telogen phase. Clinical measurements show:

• Telogen-to-anagen conversion accelerates within 4 to 6 weeks (producing the initial shed)
• Anagen duration increases measurably by 4 to 6 months
• 40 to 60% of users show regrowth as the ratio shifts back toward normal
• The effect is dose-dependent (5% outperforms 2% in most studies)

PRP (Platelet-Rich Plasma)

PRP therapy ($500 to $2,000 per session) introduces concentrated growth factors directly into the scalp. Studies show:

• Increased anagen hair count and decreased telogen count within 3 months
• Growth factor stimulation of the dermal papilla extends anagen duration
• 30 to 40% density increase in responders, partly driven by ratio improvement

Using Ratio Data in Your Tracking Strategy

Even without clinical trichoscopy, you can incorporate growth cycle awareness into your home tracking routine.

Track Shedding Patterns

Count the hairs in your shower drain or on your pillow for 7 consecutive days each month. A consistent baseline (say, 60 to 80 hairs per day) with seasonal fluctuations is normal. A sustained increase above your baseline, lasting more than 3 months, may indicate a ratio shift worth investigating.

Photograph Consistently

Monthly photos taken under identical conditions allow AI analysis to detect the indirect markers of anagen-telogen shift. Over a 6 to 12 month period, changes in the proportion of thick vs. thin hairs, overall density, and coverage area all reflect underlying cycle changes. See our guide on hair density tracking for detailed measurement techniques.

Combine With Clinical Data

If you get a clinical trichoscopy, record the exact anagen-telogen ratios for each measured zone. This gives you a precise calibration point for your home tracking data. Repeat the clinical measurement every 6 to 12 months to track the ratio directly.

Get Your Baseline Assessment

Understanding your hair growth cycle starts with knowing where you stand today. Whether you are just beginning to notice changes or you are monitoring treatment progress, consistent tracking gives you the data to make informed decisions.

Upload your tracking photos at myhairline.ai/analyze to get an AI-powered analysis of your current hair density, thickness distribution, and regional patterns that correlate with anagen-telogen balance.

Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Hair growth cycle patterns vary between individuals. Consult a board-certified dermatologist for clinical trichoscopy and personalized treatment recommendations.