Hair drug testing is commonly used when someone needs a longer lookback period than urine or oral-fluid testing can provide. A standard head-hair test generally examines the approximately 1.5 inches of hair closest to the scalp, representing roughly the previous 90 days.
That is not the only available option. Depending on the question being asked and the amount of head hair available, DNA & Drug Screening Services can coordinate approximate 30-day, 60-day, 90-day and segmented 180-day testing.
These timeframes are estimates rather than exact calendar dates. Hair grows at different rates from person to person, and recently used substances may not appear in the portion of hair that has emerged above the scalp immediately.
Hair length and testing windows
| Testing option | Head hair analyzed | Approximate period represented |
|---|---|---|
| 30-day test | 0.5 inch closest to the scalp | Most recent 0–30 days |
| 60-day test | Approximately 1 inch closest to the scalp | Most recent 0–60 days |
| Standard 90-day test | Approximately 1.5 inches closest to the scalp | Most recent 0–90 days |
| Segmented 180-day testing (two tests total) | Two consecutive sections of approximately 1.5 inches each | Segment A: 0–90 days; Segment B: 90–180 days |
The laboratory reports the shorter sections or segments separately when that testing configuration is requested and sufficient head hair is available.
Can hair testing cover 30 or 60 days?
Yes. A shorter section of head hair can be analyzed when the requested lookback period is shorter than the standard 90-day window.
For an approximate 30-day test, the laboratory analyzes the 0.5 inch of hair closest to the scalp. An approximate 60-day test uses a longer scalp-nearest section, generally about 1 inch.
Shorter-window testing may be useful when a court order, treatment plan, personal monitoring agreement or other testing requirement asks about a more recent period. The requested window should be confirmed before collection so the specimen can be documented and prepared correctly.
How 180-day segmented testing works
When enough head hair is available, 180-day segmented testing requires two laboratory tests total:
- Segment A is the section closest to the scalp. It represents approximately the most recent 0–90 days.
- Segment B is the next section moving away from the scalp. It represents approximately 90–180 days before collection.
The laboratory issues two results—one identified as Segment A and the other as Segment B. This can help show whether the findings differ between the more recent and older periods.
Segmented testing does not identify the exact date a substance was used. The reported periods are estimates based on the length and position of the hair, typical growth patterns and the laboratory’s testing protocol.
Why the timing is approximate
Scalp hair grows at an average rate of about 1 centimeter per month, but growth varies among individuals. The hair must also grow through the skin before it can be collected above the scalp. Because of that biological variation, a hair test should be understood as covering an approximate period—not as a day-by-day timeline.
Hair testing is generally better for identifying longer-term patterns than very recent use. If the main concern is possible drug use during the last several days, urine or oral-fluid testing may be more appropriate. Our staff can help determine which specimen type best fits the testing purpose.
Head hair vs. body hair
Head hair is strongly preferred for 30-day, 60-day and segmented testing because the collector must preserve the scalp end and the laboratory must know which portion is newest.
Body hair may sometimes be accepted for a standard hair drug test when sufficient head hair is unavailable. Because body hair grows more slowly and spends longer in resting phases, it may represent a much broader period—commonly estimated at approximately six months to one year, depending on the collection area and the individual’s growth cycle.
That does not mean a body-hair result can establish use during a specific month. Hair collected from an approved body area contains hairs in different stages of growth and does not provide the same scalp-to-tip timeline as head hair. The laboratory generally analyzes it as one combined specimen, so it cannot reliably be divided into 0–30, 0–60, 0–90 or 90–180-day segments. Body-hair acceptance and the period represented depend on the laboratory, test panel and collection site.
Can a hair test show the exact date?
No. Even segmented testing cannot establish a specific date of use. It may help distinguish an approximate recent period from an older period, but differences in hair growth, the timing of incorporation and laboratory methodology prevent exact dating.
Hair results also do not determine impairment, the exact amount used or how frequently a substance was used. They report whether the laboratory detected the tested substance or metabolite according to its procedures and cutoff levels.
Choosing the right testing window
Before ordering a test, consider:
- What period does the court, attorney, employer, treatment provider or requesting party require?
- Is a standard 90-day result sufficient?
- Is the goal to examine a shorter recent period?
- Are two separate 0–90 and 90–180-day results needed?
- Is enough head hair available for the requested test?
- Which substances must be included in the panel?
Panel availability and segmentation options can vary by laboratory and testing purpose. Confirm the required panel and reporting format before collection.
Hair drug testing in San Jose
DNA & Drug Screening Services provides hair drug-test collections in San Jose for personal, court-related and professional testing needs. We offer standard and specialty hair panels, shorter approximate windows when available, and segmented testing when sufficient head hair and an appropriate laboratory test are available.
Review our hair drug testing services and prices or see our complete testing price list. Please call (408) 993-9998 before visiting for a shortened or segmented hair test so we can confirm the panel, specimen requirements, reporting format and current price.
DNA & Drug Screening Services, Inc.
242 Meridian Ave, Suite C
San Jose, CA 95126
Monday–Friday, 7:30 AM–3:30 PM
Sources
- Quest Diagnostics: Workforce Health Solutions describes hair testing as identifying substance use over approximately the previous 90 days.
- NCBI Bookshelf: How hair grows notes that scalp hair grows approximately 1 centimeter per month, while individual growth varies.
Testing windows are approximate. Laboratory requirements, accepted specimen types, available panels and reporting formats may vary. This information is educational and does not replace instructions from a court, employer, attorney, treatment provider or laboratory.