> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sonohealth.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Understanding Blood Oxygen (SpO2) and Pulse Oximetry

> How a pulse oximeter works, what SpO2 means, what affects accuracy, and how to use home oxygen readings responsibly alongside how you actually feel.

A pulse oximeter is a small, painless device that clips onto your fingertip and estimates how much oxygen your blood is carrying. It's a handy way to spot-check at home — as long as you understand what the number means and what it doesn't.

<Warning>
  A pulse oximeter is a monitoring aid, not a diagnosis. If you're struggling to breathe, treat the symptoms — call 911 — regardless of what the device shows.
</Warning>

## What is SpO2?

SpO2 stands for peripheral oxygen saturation — the percentage of your hemoglobin that's carrying oxygen. For most healthy people, a [normal SpO2 is about 95–100%](/pulse-oximeter/normal-oxygen-levels). The device also displays your pulse rate in beats per minute.

## How does a pulse oximeter work?

It shines light through your fingertip and measures how much is absorbed by oxygen-rich versus oxygen-poor blood, calculating a saturation estimate in seconds. Because it reads through the skin, it's an **estimate** — accurate enough for trends in most people, but sensitive to a few conditions.

## What affects accuracy?

* **Cold hands or poor circulation** can weaken the signal.
* **Nail polish and artificial nails** (especially dark colors) can interfere — remove them or try another finger.
* **Movement** during the reading can throw it off.
* Readings can be **less reliable at very low oxygen levels** and, research has noted, **less accurate on darker skin tones** in some cases.

For the best result, warm your hands, sit still, and let the number settle.

## How to use the readings well

Watch the **trend** rather than fixating on a single number, and always weigh the reading against how you feel. A normal number doesn't override real symptoms, and a borderline number in someone who feels fine may just be a measurement issue — re-check with good technique. People with lung conditions should follow the [targets their doctor sets](/pulse-oximeter/copd-asthma-monitoring).

SonoHealth offers a fingertip **Pulse Oximeter** for simple home spot-checks of oxygen and pulse — see it at [SonoHealth.com](https://sonohealth.com/shop/).

***

**Related:** [Normal Oxygen Levels](/pulse-oximeter/normal-oxygen-levels) · [Oximetry With COPD or Asthma](/pulse-oximeter/copd-asthma-monitoring) · [Breathing Relief at Home](/nebulizer/breathing-relief-at-home)