Saline solution is a mixture of salt (sodium chloride) and water, most commonly prepared at a concentration of 0.9%. At this concentration, it closely matches the salt level of your body’s own fluids, which is why it’s called “normal” saline. That simple property makes it one of the most widely used liquids in medicine, from hospital IV bags to the bottle of nasal spray in your medicine cabinet.
How Saline Works in Your Body
Your cells sit in a constant bath of fluid that contains a precise balance of water and dissolved salts. When you introduce a liquid with a different salt concentration, water moves across cell membranes to try to equalize things, a process called osmosis. If the surrounding fluid is too dilute, water floods into cells and they swell. If it’s too concentrated, water gets pulled out and cells shrink.
Normal saline (0.9%) is considered isotonic, meaning its salt concentration essentially matches what’s already inside and around your cells. When isotonic saline enters your bloodstream or touches your tissues, there’s no net movement of water in or out of cells. Everything stays in equilibrium, which is exactly what you want when you’re replacing lost fluid without disrupting the body’s chemistry.
Normal Saline vs. Your Blood
Despite being called “normal,” 0.9% saline isn’t a perfect copy of human blood plasma. It contains 154 millimoles per liter of both sodium and chloride, giving it an osmolarity of 308 mOsm/L. Your blood plasma, by comparison, has an osmolarity of roughly 275 to 295 mOsm/L, with chloride levels between 94 and 111 mmol/L. So normal saline actually delivers more chloride than your body typically carries. For short-term use this rarely matters, but in certain hospital settings where large volumes are needed, doctors sometimes choose alternatives that more closely mirror the full mineral profile of blood.
Different Concentrations for Different Purposes
Not all saline is 0.9%. Changing the salt concentration changes what the solution does.
- Hypotonic saline (0.45%) has less salt than body fluids. Water moves from the solution into cells, which makes it useful when cells themselves are dehydrated or when sodium levels in the blood are too high.
- Normal saline (0.9%) is the standard isotonic formula used for general hydration, wound rinsing, and IV fluid replacement.
- Hypertonic saline (3% and above) has more salt than body fluids. It pulls water out of swollen tissues, so it’s reserved for serious situations like dangerously low sodium levels or brain swelling.
Common Medical Uses
In hospitals, normal saline is one of the first things reached for when a patient needs fluid. Its FDA-approved uses include replacing fluid lost to dehydration, blood loss, or infection, correcting mild sodium depletion, and restoring electrolyte balance. Because it’s isotonic, it can be delivered directly into a vein without damaging blood cells.
Outside the hospital, you’ll encounter saline in smaller, everyday forms: pre-filled nasal spray bottles, wound wash cans at the pharmacy, and contact lens rinse solutions. The concentration is the same 0.9%, just packaged differently.
Nasal Rinsing
Flushing your nasal passages with saline is one of the most effective home remedies for congestion. The salt water thins sticky mucus, washes out allergens, bacteria, and other debris, and reduces the swelling that makes your nose feel blocked. It can relieve symptoms from sinus infections, seasonal allergies, colds, flu, and COVID-19. Many people notice improvement after a single rinse, and studies show that both children and adults with allergies who rinse regularly experience better symptoms for up to three months.
You can use a squeeze bottle, neti pot, or bulb syringe. The key safety rule is never to use plain tap water. Tap water can contain trace organisms that are harmless in your stomach but dangerous in your sinuses. Use distilled water, sterile water, or water you’ve boiled for at least one minute and then cooled.
Wound Cleaning
Saline is a gentle, effective way to rinse minor cuts and scrapes. Irrigating a wound soon after it happens helps flush out dirt and debris, lowering your risk of infection without irritating exposed tissue the way soap or hydrogen peroxide can. If you don’t have saline on hand, mild soap and clean running water work as a substitute. For deeper wounds that won’t stop bleeding or look like they might need stitches, cleaning at home isn’t enough on its own.
Contact Lens Care
If you wear contact lenses, it’s important to understand what saline can and cannot do. Saline rinses lenses, but it does not disinfect them. According to the CDC, saline should only be used to rinse contacts after you’ve already cleaned and disinfected them with a separate product. Multipurpose solution, by contrast, is an all-in-one system that cleans, rinses, disinfects, and stores soft lenses. Hydrogen peroxide-based systems both clean and disinfect. Using saline alone and skipping a disinfecting step leaves bacteria and other microorganisms on the lens surface.
Making Saline at Home
A basic saline solution is simple to prepare: dissolve about half a teaspoon of non-iodized salt into one cup (8 ounces) of distilled or previously boiled water. This gets you close to the 0.9% concentration used in commercial products. Stir until the salt dissolves completely.
Homemade saline works well for nasal rinsing and for cleaning minor wounds. It does not work as a sterile medical product, so it shouldn’t be used for anything involving the eyes or for irrigating deep or serious injuries. Make a fresh batch each day, because bacteria can grow in salt water that sits at room temperature. Store-bought sterile saline, available at most pharmacies for a few dollars, is the safer choice when you need something shelf-stable or more reliably clean.