FAQ: How Can my Paternity Test Samples Get Contaminated?

Nov 18, 2019 | Blog, DNA test, Paternity, Paternity Test

How Can Paternity Test Samples Get Contaminated? 

 “Uh oh. I think I messed up my paternity test.”

Our customer-service specialists often hear this statement from clients who call in, worried about whether or not the samples they submitted for their at-home paternity test or other relationship analysis might have been contaminated.

When you order a test, you and the lab form a partnership in the proper handling of these samples.  As a highly-accredited laboratory, we take our responsibility seriously and have strict processes in place to ensure samples are not contaminated at the lab level.  As a participant in the test, your job is to get your samples to the lab in the best condition possible.


Collecting DNA with cheek swabs is easy and painless, but do it with care.

DNA collected via cheek swabs is every bit as effective for testing as a blood sample. The process involves vigorously rubbing the inside of the cheek for 30-60 seconds for each swab included in the kit to ensure enough cells are collected for testing. So how might samples for a paternity test get contaminated?

1. Eating, Drinking, or Smoking before Swabbing

All participants in a paternity test should refrain from eating, drinking, or smoking for one hour prior to swabbing—this is also true for nursing infants. Although having foreign residue in your mouth won’t change your DNA, it can definitely affect the quality of the samples by degrading them, making it difficult or impossible for robots at the lab to extract usable DNA from the swabs.
GOOD NEWS: This type of contamination doesn’t affect the results of your paternity test because the lab simply stops testing and asks for new samples before proceeding with analysis. New testing materials are sent to you at no charge.
BAD NEWS: It’s a source of stress for you because your results will be postponed and you have to wait a little longer.
PREVENTION TIPS: If one of the participants eats, drinks, or smokes prior to swabbing, just delay swabbing for an hour.


2. Cross-Contamination during DNA Collection

To maintain the swabs’ integrity, do your best to avoid the following:

  • Handling the soft ends of the swabs
  • Dropping swabs
  • Putting swabs from two different people in the same envelope

GOOD NEWS: If contamination occurs as a result of any of these actions, the lab will catch it and ask for new samples.
BAD NEWS: Again, you have to wait longer for results if the lab asks for DNA recollection.
PREVENTION TIPS: Handle swabs with care and follow all kit directions.


3. Mailing Wet Envelopes or Re-Using Plastic Packaging

Wet Envelopes

It’s not at all unusual for a little excess saliva to get mixed in with cheek cells when collecting DNA for a paternity test. As a result, the sample and even the mailing envelopes may become a little wet. If mailed while damp, packaging could tear and swabs can become contaminated.

GOOD NEWS: DNA samples can simply be collected again.

BAD NEWS: There is a delay in issuing results.


  • The swabs for a paternity test are designed to collect cheek cells—not saliva. Be sure to only swab the insides of your cheeks and avoid gum areas
  • If a swab is “too wet,” hold the swab up and wave it in the air for 60 seconds to dry it a bit before placing in the paper sample envelope
  • If an envelope still gets a little wet, lay it on a clean counter and allow it to air-dry prior to mailing

Re-using Plastic Packaging

DNA is organic material and is therefore susceptible to becoming moldy under adverse conditions. Mold degrades DNA on a swab extremely fast, and this kind of contamination makes using the sample for testing impossible. If you put swabs containing DNA back into the plastic packaging the DNA came in, the sample can’t “breathe” and the consequence is almost always rapid mold growth—even if you mail samples off right away.

GOOD NEWS: New DNA samples can be collected.

BAD NEWS: You have to wait longer for results

PREVENTION TIPS: Once you’ve collected the DNA, make sure the swabs have been air-dried as much as possible and then place them in the paper envelopes provided in your kit.

 Final Thoughts about Swab Contamination

It’s important to remember that swab contamination can never “change” the results of a paternity test or “change the DNA.” So there’s no need to worry! If contamination occurs, the lab always catches it, and the worst that can happen is the lab will ask for samples to be collected again. Just be sure to carefully follow all instructions that come with your paternity test, and feel free to reach out to us if you have any questions or concerns.

Call us at 800-929-0847: We’re here to help.



  1. Alicia

    How long does a Paternity takes before no good check the blood test

    • DDC

      Hi, Alicia. I’m not sure I understand your question?


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