The usual culprits are eating, drinking, smoking, gum or brushing too soon before you spit, not enough liquid saliva (bubbles don't count), a stabilizing buffer that wasn't released or mixed, a loose cap, and a kit that was never registered. Wait at least 30 minutes, fill to the line, cap tightly, shake, register, and mail it promptly.
If a sample does fail, AncestryDNA, 23andMe and Dante Labs all describe free replacement kits on their help pages, though the details differ.
- Why a sample can fail
- Before you spit: the 30-minute rule
- Collect enough saliva, not just bubbles
- Release and mix the stabilizing buffer
- Register the kit before you mail it
- Shipping delays and old kits
- Special cases worth knowing
- Quick checklist
- What happens if your sample fails
- If you're still choosing a test
- Common questions
Check which kit you have. As of October 25, 2026, Dante Labs’ homepage describes a finger-prick blood spot kit for its whole genome test, while its help center still has saliva instructions. The saliva advice below applies to saliva kits; for a blood spot kit, follow the instructions in the box.
Why a sample can fail
A spit kit looks simple, but the lab needs enough clean, well-preserved DNA to work with. Saliva contains cells, and those cells contain your DNA. Anything that leaves too little saliva in the tube, contaminates it, or lets it break down in transit can leave the lab short. For a walk-through of what the lab does once your tube arrives, see what happens to your saliva sample after sequencing.
Dante Labs' support center describes three checks every sample has to pass before sequencing: volume, DNA yield after extraction, and purity. Other companies word it differently, but the reasons they list fall into the same few buckets.
AncestryDNA's help center names the common ones: a cap problem that lets saliva leak out during shipping, saliva and stabilizing fluid that weren't fully mixed, too much or too little saliva, contamination (food or drink particles, toothpaste, chewing tobacco and other materials), and DNA from more than one person. It also says some saliva is naturally too thick or too thin, and that some failures happen in the lab for reasons unrelated to how you collected. 23andMe makes a similar point: because of biological variability, some people simply don't have a high enough concentration of DNA in their saliva, and it isn't always known why some samples are harder to analyze.
A failed sample is not a health result. Dante Labs' support article says plainly that a failed sample says nothing about your health. It's a lab-quality problem, not a finding about you.
Before you spit: the 30-minute rule
The most consistent advice across providers is to keep your mouth clear of everything for about half an hour first. Here's how three companies phrase it on their own help pages:
- 23andMe: don't eat, drink, smoke, chew gum, brush your teeth or use mouthwash for at least 30 minutes before giving a sample.
- Dante Labs: don't eat, drink, smoke or brush your teeth for 30 minutes beforehand.
- AncestryDNA: brush your teeth or use mouthwash 30 minutes before, and don't eat, drink, smoke, or chew gum or tobacco until you've collected your sample.
Food, drinks and toothpaste are exactly the kind of contamination labs list as failure causes. Dante's support team also names eating shortly before collection as one reason behind low DNA yield.
The easiest way to get this right is to plan the moment. Many people collect soon after waking, before breakfast, coffee or brushing. If you've already eaten, set a timer for 30 minutes and wait it out.
Collect enough saliva, not just bubbles
Under-filling is the big one. Dante Labs says most of its recollection requests come from under-filled tubes rather than anything biological.
- Measure the liquid, not the foam. 23andMe recommends about 2 mL (roughly half a teaspoon), with your saliva just above the fill line. AncestryDNA says your saliva, not bubbles, should reach the wavy line, and bubbles can sit above it. Dante also asks for about 2 mL, not counting bubbles.
- Don't overfill. AncestryDNA warns against this, and its list of failure reasons includes too much saliva as well as too little.
- Don't drag it out. 23andMe says the full sample should be collected within 30 minutes, and that waiting longer may reduce the yield and quality of your DNA.
- Get saliva flowing. Dante suggests rubbing the outside of your cheeks for a few seconds and letting saliva pool in your mouth before you spit.
- One person, one tube. Never share a tube, and keep anything that isn't saliva out of it.
Spitting enough can take longer than you expect, especially if your mouth is dry. Let the bubbles settle for a moment so you can see where the liquid really sits before you decide you're done.
Release and mix the stabilizing buffer
Most spit kits have a funnel lid or cap that releases a stabilizing liquid into the tube. That liquid protects your DNA on its trip to the lab. If it never reaches the saliva, or isn't mixed in, the sample is more likely to fail.
- AncestryDNA: swap the funnel for the cap containing blue stabilizing fluid, twist it tightly until the fluid releases, then shake the tube for five seconds.
- Dante Labs: screw the funnel closed so the blue stabilizing liquid releases, then shake for five seconds.
- 23andMe: release the funnel's contents into the tube right away, then remove and discard the funnel lid and put the tube cap on securely before mailing.
A loose cap is its own problem: AncestryDNA lists cap problems that lose saliva during shipping as a common failure reason. Twist until it's tight, then hold the tube upside down for a second to check for leaks before it goes in the bag.
Register the kit before you mail it
Registration (some companies call it activation) links the barcode on your tube to your account. Skip it and the lab may not be able to match the sample to you.
- AncestryDNA asks you to register your kit before collecting your sample.
- Dante Labs says to register the barcode in your Dante ID account before mailing, because an unregistered tube can't be linked to a profile.
- 23andMe asks each person to use the tube from the kit they have registered or intend to register.
If two people in your household are testing at the same time, keep the kits apart and make sure each barcode is registered to the person who actually spat into that tube. Snapping a photo of each barcode before you seal the mailer makes any later support conversation much easier.
Shipping delays and old kits
Once saliva is mixed with the buffer, it's fairly hardy. 23andMe says a stabilized sample is stable from -4°F to 122°F. Dante Labs says stabilized samples stay usable at room temperature for up to 30 days, so a weekend in a mailbox is fine. That still isn't a reason to leave the box in a drawer.
- Mail it soon. 23andMe recommends shipping at your earliest convenience.
- Use the route the company asks for. 23andMe says to drop its prepaid package in a US Postal Service mailbox, and not to take it to a mail center or deliver it directly to the distribution center or lab, which can cause delays.
- Check the date on the tube. 23andMe tubes carry a "Collect saliva by" date, which marks the kit's expiration. Collect before then.
- Late is better than never. AncestryDNA says that even if time has passed since you collected, you should still send the sample so it can try to process it.
Sending a kit across borders adds customs time and paperwork. Our guide to international shipping and customs for DNA kits covers what to expect.
Special cases worth knowing
A few situations can cause trouble no matter how carefully you spit. AncestryDNA says people who have received a bone marrow or stem cell transplant from another person should not submit a sample, since it can contain DNA from more than one person. It also notes that some medical treatments, such as chemotherapy, can temporarily affect DNA quality.
If either applies to you, contact the company before you collect. If you're testing for a health reason, ask your clinician or a genetic counselor which sample type makes sense. Our comparison of saliva, blood and cheek swab samples explains the trade-offs.
Quick checklist
| Common mistake | What to do instead |
|---|---|
| Eating, drinking, smoking, gum or brushing just before | Wait at least 30 minutes, or follow your kit's exact wording |
| Counting bubbles as saliva | Fill to the line with liquid saliva; let foam settle and check again |
| Overfilling the tube | Stop at the line your kit shows |
| Buffer not released or mixed | Close the cap or funnel fully, then shake as instructed |
| Loose cap | Twist until tight and check for leaks |
| Kit not registered | Register or activate the barcode before mailing |
| Box left sitting for weeks | Mail promptly, the way the company specifies |
| Expired kit | Check any "collect by" date on the tube first |
What happens if your sample fails
You'll usually hear by email. The major companies we checked describe a replacement process rather than leaving you stuck, but terms differ and can change, so read the email closely and check the company's current help page.
- AncestryDNA says that if the lab can't process your sample, it will send a free replacement kit. You request it from the email or your DNA homepage, it says the kit should arrive within 10 business days of ordering, and the original kit can no longer be used.
- 23andMe lists a free replacement when the lab couldn't successfully analyze a first saliva sample. The replacement is tied to your profile and must be registered before you send it back. If a second sample also fails, it says you can request a refund instead, and a replacement kit is no longer an option.
- Dante Labs says replacement kits are free and ship within one business day. It says the processing clock restarts when the new sample reaches the lab, which typically adds three to four weeks, and that after a second failure it moves you to a cheek-swab kit.
Before you collect the second sample, reread the instructions from start to finish. Since under-filled tubes are the most common cause Dante describes, start there: give yourself more time, more saliva and a full 30-minute wait.
If you're still choosing a test
Sample type is worth asking about before you buy. Dante Labs, for example, currently describes a finger-prick dried blood spot for its whole genome test, and its support center has guides for both blood and saliva collection. Our list of questions to ask before buying whole genome sequencing covers this and the other things worth checking.
Want the full 30× genome instead of a partial test?
Dante Labs sequences your whole genome and lets you download the raw FASTQ, BAM and VCF files. When we checked on October 25, 2026, it listed the test from $449 with 90+ reports included and results in 6–8 weeks.
Check Dante’s current offer →Code: GENOMEAffiliate link. Prices and promotions change, and codes may not combine with sitewide sales. Confirm the final price at checkout.
Common questions
How long should I wait after eating before a DNA saliva test?
23andMe and Dante Labs both say at least 30 minutes after eating, drinking, smoking or brushing. AncestryDNA says to brush or use mouthwash 30 minutes before and not to eat, drink, smoke or chew gum until you've collected. Follow the exact wording on your own kit.
Can I drink water before spitting?
The help pages we checked say not to drink anything during the waiting period and don't carve out an exception for water, so the safest choice is to wait the full 30 minutes.
Do bubbles count toward the fill line?
No. AncestryDNA says your saliva, not bubbles, should reach the line, and Dante Labs asks for about 2 mL not counting bubbles. Let the foam settle and check the liquid level.
How long can I wait before mailing my sample?
Mail it as soon as you can. Dante Labs says stabilized samples stay usable at room temperature for up to 30 days, and 23andMe tubes carry a “Collect saliva by” date. If time has already passed, AncestryDNA says to send it anyway.
Does a failed sample mean something is wrong with my DNA?
No. A failed sample is a lab-quality issue, often too little DNA in the tube. Dante Labs says a failure says nothing about your health, and 23andMe notes some people naturally have lower DNA concentration in saliva.
Sources and verification
We read AncestryDNA's, 23andMe's and Dante Labs' official help pages on October 25, 2026, including Dante's support articles on saliva collection and sample recollection. None of these companies publishes an overall failure rate, so we don't give one, and replacement or refund terms can change, so check the current page for your kit.
Medical disclaimer. GenomeTesting.org publishes educational content about genetics and consumer genomic testing. Nothing here is medical advice, a diagnosis, or a substitute for care from a qualified clinician or genetic counsellor. Decisions about testing, treatment, or interpreting your own results should be made with a healthcare professional who can see your full history.
Affiliate disclosure. Some links on this page are affiliate links. If you buy through them we may earn a commission at no extra cost to you. This never changes which products we recommend or what we say about them.