How Long Does Weed Stay in Your Hair

Written by Brandon Topp

October 15th, 2025

Hair tests detect THC for up to 90 days using the 1.5 inches of hair closest to your scalp.

There's a 7-10 day delay before cannabis use appears in new growth, and body hair can extend the detection window even further.

If you're calculating whether your last use will show up, you need all three pieces of this timeline puzzle working together.

The 90-day rule you've heard about isn't wrong, but it's incomplete.

Labs analyze hair at an average growth rate of 0.5 inches per month, which means 1.5 inches represents roughly three months of history.

Add the initial lag before metabolites appear, and you're looking at a specific window you can actually calculate.

This guide walks through timeline scenarios based on your exact usage pattern.

We'll explain why body hair changes everything, which factors affect your individual results, and what happens when common strategies like detox shampoos fail.

Table of Contents

• THC Stays in Hair for 90 Days From Your Scalp

• One-Time Use vs Daily Smoking Detection Rates

• Why Your Metabolism and Hair Type Matter

• Body Hair Reveals Longer Drug History

• What Happens During Hair Follicle Testing

• Will You Pass? Timeline Scenarios From 30 to 90 Days

• Why Detox Shampoos Keep Failing

• Hair Testing Compared to Urine and Blood Tests

• What Testing Facilities Actually Measure

• What You Know Now That Others Don't

THC Stays in Hair for 90 Days From Your Scalp

Hair follicle tests analyze the 1.5 inches of hair closest to your scalp. At an average growth rate of 0.5 inches per month, this sample represents approximately 90 days of cannabis use history.

The 90-day window starts when THC metabolites actually enter your hair shaft, not when you consume cannabis.

After you smoke, vape, or eat THC products, it takes 7-10 days for metabolites to appear in new hair growth.

Here's the math: if you used cannabis 75 days ago, subtract the 7-10 day lag and you're looking at 65-68 days of potentially detectable metabolites in your hair.

A standard 1.5 inch sample would capture this usage.

Some labs take up to 2 inches of hair instead of the standard 1.5 inches.

This extends the detection window to 120 days instead of 90 days, catching use that happened four months ago instead of three.

The Growth Rate Variable

Not everyone's hair grows at exactly 0.5 inches per month.

Factors like age, genetics, and overall health can speed up or slow down growth rates slightly.

Faster growth means your 1.5 inch sample might only represent 80 days instead of 90.

Slower growth could push it to 100 days or more.

One-Time Use vs Daily Smoking Detection Rates

Hair tests reliably detect patterns of regular cannabis use across the full 90-day window. Single or infrequent use presents a different detection picture entirely.

The test works by measuring THC-COOH metabolites that accumulate in your hair shaft over time.

Daily smokers build up consistent metabolite levels that labs easily detect, while one-time users may fall below detection thresholds.

Consider these scenarios: Someone who smoked daily for two months, then stopped 60 days before testing, will almost certainly test positive.

Someone who hit a vape once 60 days ago faces lower detection risk, though not zero risk.

Why Light Use Creates Uncertainty

The question we hear most is whether two hits 45-60 days ago will register on a test.

Lower metabolite concentrations from infrequent use can fall below lab cutoff thresholds, especially as time passes and hair growth dilutes the sample.

This doesn't mean you're safe after light use.

Lab sensitivity varies, individual metabolism differs, and the 7-10 day incorporation window means your "one time" use might hit during a period of faster metabolite production.

Why Your Metabolism and Hair Type Matter

Darker, coarser hair retains more THC metabolites than lighter, finer hair. The melanin in dark hair binds to cannabis metabolites more readily, creating higher concentrations that tests detect more easily.

Someone with black hair who used cannabis once might test positive while someone with blonde hair using the same amount might not.

This biological reality explains conflicting stories about identical usage patterns producing different results.

THC is fat-soluble, which means it stores in body fat before gradually releasing into your bloodstream.

Higher BMI and slower metabolism extend how long metabolites circulate in your system and deposit into growing hair.

Consumption Method Differences

Edibles produce different metabolite profiles than smoking or vaping.

When you eat cannabis edibles, your liver converts THC into 11-hydroxy-THC, which can create different detection patterns.

Hair tests focus on long-term use patterns rather than pinpointing specific consumption methods.

Whether you smoked flower or ate gummies matters less than how frequently you consumed and how much.

Body Hair Reveals Longer Drug History

If your head hair is too short for testing, collectors use body hair from your arms, legs, chest, or underarms.

This isn't a backup option—it's standard testing procedure that catches many people off guard.

Body hair grows differently than scalp hair. While head hair replaces itself every 2-6 years, body hair can remain in the growth phase for 6-12 months or longer before shedding.

A 1.5 inch sample of arm hair doesn't represent 90 days like it would from your scalp.

It could capture 6 months, a year, or even longer depending on your individual hair growth cycles.

Why Shaving Your Head Backfires

Showing up to a drug test with a freshly shaved head signals tampering.

Collectors simply move to body hair collection, which often works against you by extending the detection window.

Some facilities note "insufficient head hair" on test forms, which itself raises questions. You're trading a 90-day window for a potentially longer one while simultaneously drawing attention to your results.

What Happens During Hair Follicle Testing

The collector cuts a small sample of hair close to your scalp, typically from the crown area where growth is most consistent.

The actual follicle isn't tested—the term "hair follicle test" refers to testing the hair shaft itself.

Labs wash samples before testing to remove external contamination.

This step addresses concerns about secondhand smoke exposure or surface contact with cannabis, though these rarely cause confirmed positives.

The initial screening uses an immunoassay test.

Positive results move to gas chromatography-mass spectrometry (GC-MS) confirmation testing, which provides definitive identification of THC metabolites.

Sample Length Requirements

Standard testing requires 1.5 inches of hair measured from the scalp.

If you have shorter hair, some facilities test what's available and note the reduced detection window on results.

Others refuse testing until sufficient hair growth allows proper sample collection.

Requirements vary by testing facility and the entity requesting the test.

Will You Pass? Timeline Scenarios From 30 to 90 Days

Let's calculate your risk based on specific situations. Remember to account for the 7-10 day lag, the 1.5 inch sample covering 90 days, and the possibility of body hair testing.

Scenario 1: Single Use 60 Days Ago

You hit a vape or ate an edible once, 60 days before your test. After the 7-10 day delay, metabolites entered your hair approximately 50-53 days ago.

A standard 1.5 inch head hair sample would capture this usage.

Your risk depends on metabolite concentration from that single use, your hair type, and lab sensitivity. Lower concentration means higher chance of falling below detection thresholds, but it's not guaranteed.

Scenario 2: Occasional Use, Last 45 Days Ago

You used cannabis a few times over two months, with your last use 45 days ago.

Your earlier use (60-90 days ago) sits right at the edge of or beyond the standard detection window.

The most recent use 45 days ago would definitely appear in testing after accounting for the lag. Your occasional pattern creates moderate metabolite levels that labs typically detect.

Scenario 3: Daily Use Stopped 75 Days Ago

You stopped regular daily consumption 75 days before testing.

After the 7-10 day delay, you have approximately 65-68 days of clean hair growth.

The bottom portion of your 1.5 inch sample still contains metabolites from your regular use period. Labs will detect this daily use pattern even though you've been clean for more than two months.

Scenario 4: Test in Three Weeks, Light Use Pattern

You occasionally use THCa flower or other cannabis products, most recently two weeks ago.

With only three weeks until testing, you don't have enough clean growth to outpace the detection window.

The 7-10 day lag means your two-week-old use is just now entering your hair shaft. You need at least 90 days of abstinence plus hair growth to clear regular detection.

Body Hair Changes Everything

For every scenario above, add this caveat: if collectors use body hair instead of head hair, your detection window extends significantly.

That "60 days ago" single use might still be detectable in arm hair that's been growing for 8-10 months.

Why Detox Shampoos Keep Failing

THC metabolites sit inside your hair shaft, not on the surface.

Shampoos can't penetrate deep enough to remove embedded compounds without destroying the hair structure itself.

The Macujo method and similar protocols involve harsh chemical treatments—bleaching, multiple washes, and aggressive scrubbing. Users report spending hundreds of dollars and damaging their hair, only to fail their tests anyway.

Lab washing procedures before testing already remove surface contamination.

Any metabolites detected after this cleaning process came from inside the hair shaft, where they arrived through your bloodstream.

The Shaved Head Problem

When you show up completely bald to a hair test, collectors follow established procedures. They check for body hair on your arms first, then legs, chest, or underarms.

If you've shaved everything, the collector notes this on the test report.

Some employers or testing authorities interpret total body shaving as a refusal to test, which can carry the same consequences as a positive result.

Hair Testing Compared to Urine and Blood Tests

Different test types capture different windows of cannabis use.

Saliva tests detect use within the last 24-72 hours, making them effective for checking recent consumption but useless for longer patterns.

Blood tests show use within the previous 12-48 hours. They're most common in legal situations or accident investigations where immediate impairment matters.

Urine tests remain the workplace standard, detecting use from 3-4 days for single use up to 30+ days for heavy regular use.

Most employees face urine testing, not hair testing.

Why Employers Choose Hair Tests

Hair testing costs more than urine testing but provides a much longer detection window.

Employers in transportation, trades, certain finance roles, and security-sensitive positions use hair tests to see patterns of use rather than isolated incidents.

You can't substitute or dilute a hair sample like you might with urine.

The supervised collection and sealed chain of custody make tampering nearly impossible.

Industries with federal oversight, commercial driving requirements, or safety-critical roles commonly mandate hair testing. Office jobs and most retail positions stick with standard urine tests.

What Testing Facilities Actually Measure

While 1.5 inches is the standard sample length, some labs take 2 inches when available.

Others have specific policies about minimum hair length or body hair protocols.

The lab you're sent to might differ from what your friend experienced.

Quest Diagnostics, LabCorp, and other major testing companies each have their own standard operating procedures.

Some employers request extended panels that test for additional substances beyond the standard five or ten drug categories.

Others specify collection site (head vs body hair) in their testing orders.

Important Disclaimer: This information is for educational purposes only. We are not a medical or legal authority and cannot provide advice about drug testing or employment situations. Consult with appropriate licensed professionals for guidance specific to your circumstances.

Confirming Your Specific Test Parameters

If you know which facility will conduct your test, contact them to ask about their standard sample length and collection procedures.

Some facilities answer general questions about their testing process without discussing specific results.

Understanding whether they typically use 1.5 or 2 inches, and under what circumstances they collect body hair, helps you calculate your actual risk more accurately.

What You Know Now That Others Don't

Hair drug testing operates on three timelines working together:

The 7-10 day delay before use appears in new growth, the 1.5 inch sample representing 90 days at average growth rates, and the wildcard of body hair potentially extending detection far beyond three months.

Your frequency of use matters more than any product, method, or strategy.

Regular daily use creates consistent metabolite levels that tests reliably detect across the full window. Single or occasional use might fall below detection thresholds, though never with certainty.

No shampoo, treatment, or hack reliably removes metabolites from inside your hair shaft.

The only dependable path to passing involves abstaining long enough for clean hair to grow and replace contaminated sections, which takes the full 90+ day period.

If you're subject to testing, verify the specific parameters with your testing facility. Ask about sample length, body hair policies, and detection windows.

Make decisions based on your actual situation rather than general timelines or online success stories.

Understanding how hemp-derived THC products work can help you make informed choices about your cannabis use.

At Mood, we believe in transparent education about our federally legal products and the realities of drug testing.

Your choices are your own, but they should be informed choices based on accurate information about detection windows, testing procedures, and the factors that influence your individual results.