How Much Hair Is Needed for Hair Analysis?

You do not need a large bundle of hair for an MPU hair analysis. What matters is a clearly defined length and sufficient strand thickness. The laboratory must reliably assess alcohol or drug consumption over several months. A few carefully collected strands from the back of the head are sufficient. This article explains how many strands are needed, the required length and why pencil thickness matters, helping you check whether your hair is suitable before the appointment.

Key points at a glance

• An MPU hair analysis usually requires 2–3 strands approximately as thick as a pencil.
• The strands are cut close to the scalp at the back of the head.
• For alcohol, EtG, the laboratory examines a maximum of 3 cm, corresponding to approximately 3 months.
• For drugs, a maximum of 6 cm is examined, covering around 6 months.
• Only about 10–50 mg from the collected sample is actually analysed, making strand length and thickness particularly important.

How much hair does the laboratory need for an MPU analysis?

Generally, 2–3 pencil-thick strands cut close to the scalp at the back of the head are sufficient. For alcohol, up to 3 cm, around 3 months, is examined; for drugs, up to 6 cm, around 6 months. Ultimately, only approximately 10–50 mg is actually analysed in the laboratory.

Practical tip: Hair analysis is the simplest way to obtain proof of abstinence

How much hair the laboratory actually needs for the MPU

Many people worry that large amounts will be cut off. This is not the case. The laboratory needs only a small, carefully collected quantity. In practice, 2–3 strands are usually used.

These should be approximately pencil-thick. They must also be cut at the back of the head as close to the scalp as possible, capturing precisely the sections representing the relevant period. Your hairstyle therefore remains largely intact while the laboratory receives enough material for reliable analysis.

Why pencil-thick strands matter

The requirement for pencil thickness may initially seem abstract, but it has a clear purpose. A strand this thick contains many individual hairs, ensuring enough material for analysis.

Individual hairs can break or come loose during sample preparation. If the strand is approximately pencil-thick, this has little effect. The thickness also allows consistent measurement of substance concentrations. Both length and thickness are therefore important quality factors.

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Hair length and the detection period for alcohol (EtG)

For alcohol abstinence, the breakdown product ethyl glucuronide is measured in hair. Length plays a central role. A maximum of 3 cm is examined for an alcohol-related MPU hair analysis, corresponding to approximately three months.

Longer hair is often collected, but only this length is used in the laboratory, keeping the period clearly defined. If you need evidence across several periods, several 3 cm segments are collected at different appointments. It is therefore important that hair in the relevant area is at least 3 cm long.

Hair length and the detection period for drugs

Longer segments are used for drugs. For an MPU drug hair analysis, the laboratory generally examines a maximum of 6 cm, covering approximately six months.

This allows consumption to be assessed over half a year. Hair may be longer overall, but only the section extending 6 cm from the scalp is analysed. Longer abstinence periods therefore require multiple samples at different appointments.

It is consequently important to have enough length at the back of the head to reach those 6 cm reliably.

What happens to the 10–50 mg of hair in the laboratory?

The visible amount cut off often appears greater than what is actually used. Only approximately 10–50 mg from the collected sample is later analysed, a very small quantity.

The laboratory selects precisely the section of the required length. It is washed, cut up and chemically prepared. Relevant substances such as EtG or drug breakdown products are then measured. The remainder of the collected hair is not needed further. Although the visible amount may seem noticeable, only a small portion is analytically decisive.

Why collection site, length and thickness must all be appropriate

A rough quantity estimate is not enough for a reliable result. The collection site matters greatly. Strands can usually be taken discreetly from the back of the head, where growth is often denser and more uniform.

Cutting close to the scalp captures the most recent growth. Only then do hair length and the evidence period correspond properly. With the appropriate site, length and thickness, the laboratory can interpret values reliably. Reputable providers therefore follow these requirements strictly.

How to prepare your hair for collection

Elaborate preparation is generally unnecessary. Above all, hair at the back of the head must be long enough: at least 3 cm for alcohol evidence and 6 cm for drugs. Avoid drastic haircuts shortly before the appointment.

This preserves the necessary segment. Discussing the collection area with the institute or doctor beforehand can help. Knowing that 2–3 pencil-thick strands are sufficient allows you to attend more calmly.

The golden rule of hair length: 3 cm versus 6 cm

When asking “How much hair is needed for hair analysis?”, precise length is crucial because it documents the abstinence period. The procedure follows the rule of thumb of 1 cm growth per month. For alcohol abstinence, EtG, no more than 3 cm from the scalp may be examined, covering three months.

For drug abstinence, a maximum of 6 cm is permitted, documenting six months. Under CTU criteria, longer segments may not be analysed, ensuring unambiguous results.

Cosmetic treatment: dyeing, tinting and bleaching

Caution: cosmetically treated hair can distort results Bleaching, dyeing or tinting can destroy or break down substances incorporated in the hair. Such hair therefore effectively answers “How much hair is needed?” with “none suitable”.

Dyed or bleached hair is generally not permitted for alcohol testing with EtG. For drug testing, the first sample may be cosmetically treated, but subsequent samples must consist of untreated new growth. Otherwise, you must switch to urine screening.

Forensic thresholds: cut-offs

Hair quantity and length provide only the basis for analysis. The laboratory measures not just whether consumption occurred but how much. Alcohol analysis measures EtG, with results expressed in picograms per milligram of hair (pg/mg).

The critical cut-off is 5 pg EtG/mg hair. Values above this are interpreted as consumption and produce an unfavourable abstinence result. Only results below the threshold demonstrate the abstinence required for the MPU.

Conclusion

An MPU hair analysis needs less hair than many people fear. Appropriate length, thickness and correct collection matter most. If you have 2–3 pencil-thick strands of sufficient length at the back of your head, you are usually well prepared.

This avoids additional laboratory requests, saves time and stress and improves the chance of trouble-free recognition of your evidence. Find out early, clarify questions with the laboratory and approach MPU preparation confidently. Your hair can become a decisive advantage.

Sources:

• TÜV NORD: FAQ on Proof of Abstinence Through Hair Analysis
• University of Zurich, Forensic Medicine: Detecting Psychotropic Substances (PDF)
• Labor Enders: Information About Forensic Hair Samples

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FAQ

Exactly how much hair is required?

Generally, two or three bundles approximately as thick as a standard pencil are needed. In laboratory terms, this corresponds to at least 100 milligrams of material.

How long must my hair be for twelve months of drug evidence?

You need two consecutive analyses six months apart. Since no more than 6 cm, representing six months, may be tested each time, hair should be at least 6.5 cm long at collection.

Where on the head is the hair cut?

Hair is preferably cut at the back of the head, near the occipital prominence, because growth is generally most regular there. Collection is immediately adjacent to the scalp.

Which hair may not be used for alcohol evidence?

Armpit hair, pubic hair and other body hair are not permitted for EtG evidence in the MPU. Scalp hair must be used.

What happens if my hair is too short?

If hair is too short for the desired period, the remaining abstinence period must be documented through urine screening. This is the only way to cover the missing months until sufficient length is available again.

Will hairspray or gel distort the analysis?

No. Normal cosmetics such as gel or hairspray do not distort analysis of substances inside the hair. The laboratory routinely cleans the outside of the hair before testing.

What is the difference between analysis lengths of 3 cm and 6 cm?

A maximum of 3 cm is accepted for alcohol abstinence through EtG, representing three months. A maximum of 6 cm is accepted for drug abstinence, representing six months.

How much of the sample is actually examined?

Only a very small amount is weighed from the complete strand, typically 10–50 milligrams. The remainder is kept as a reserve, or B sample, for possible reanalysis.

Why is cutting close to the scalp important?

Substances are incorporated at the hair root. The assessor needs the segment closest to the beginning of the abstinence period to document it continuously, making close-to-scalp cutting important.

Can I use armpit or beard hair for drug testing?

Body hair, including beard, chest or armpit hair, is permitted only in exceptional cases where scalp hair is unavailable. It is less precise because its growth does not follow the one-centimetre-per-month rule.