Sometimes exclusive breast-feeding isn't possible or practical. Until age 1, formula-feeding is the next best choice. Here's what you need to know about choosing and using infant formula.

All commercial infant formulas are nutritionally sound and designed to support your baby's growth and development. Most babies thrive on cow's milk formula, but some babies fare better with other types of infant formula.

• Cow's milk formula. Most infant formula is made with cow's milk that has been altered to closely resemble breast milk. The alteration gives the formula the right amount of carbohydrates and the right percentages of protein and fat. The alteration also makes the formula easier to digest. Remember that regular cow's milk isn't a substitute for infant formula. Pasteurized goat's milk and evaporated milk aren't either.
• Soy-based formula. Soy-based formula is an alternative for babies who are allergic to the proteins in cow's milk formula or who can't tolerate lactose, a sugar naturally present in cow's milk. If you choose to use soy products, be sure to use a soy-based infant formula — not soy milk.
• Protein hydrolysate formula. This type of formula is meant for babies who have a family history of milk allergies. It's easier to digest and less likely to cause allergic reactions than standard cow's milk formula because the proteins it contains are broken down in a process that mimics digestion.

More specialized infant formulas are available for premature infants and babies who have specific medical conditions.

You can choose between powdered, concentrated liquid and ready-to-use infant formulas. Which is best depends on your budget and lifestyle.

• Powdered formula. Powdered formula is the least expensive type of infant formula. Each scoop of powdered formula must be mixed with a specific amount of water.
• Concentrated liquid formula. Some parents prefer concentrated liquid formula. It must also be mixed with a specific amount of water.
• Ready-to-use formula. As the name implies, ready-to-use formula doesn't need to be mixed with water. It's the most convenient type of formula, but also the most expensive — especially when packaged in disposable bottles.

As with most consumer products, brand-name infant formulas cost more than generic brands. But that doesn't mean that brand-name formulas are better. All infant formulas sold in the United States must meet the nutrient standards set by the Food and Drug Administration (FDA). Although manufacturers may vary somewhat in their formula recipes, the FDA requires that all formulas contain the same nutrient density.

Commercial infant formulas contain recommended amounts of many vitamins, but not all formulas contain iron. The American Academy of Pediatrics recommends iron-fortified formula for all formula-fed infants. Still, it's a good idea to check with your baby's doctor to decide what's best for your baby.

Some infant formulas are enhanced with docosahexaenoic acid (DHA) and arachidonic acid (ARA). These substances are omega-3 fatty acids found in breast milk and certain foods, such as fish and eggs. DHA and ARA are thought to be important for infant eyesight and brain development.

Infants can make DHA and ARA from other fatty acids in their diet, including the fatty acids in all commercial infant formulas. However, it's not clear whether infants can convert these components into optimal amounts of DHA and ARA. Some research suggests a benefit from adding DHA and ARA directly to infant formula — but other research has shown no benefit.

Whichever type of infant formula you choose, proper preparation and refrigeration are essential. Follow these steps:

• Wash your hands and utensils. Before preparing formula, wash your hands with soap and water. Be sure all the utensils you'll use are clean, too, including bottles and nipples. You may want to sterilize bottles and nipples before using them for the first time. After that, cleaning them in the dishwasher or washing them by hand with soapy water is enough. If you're opening a new can of formula, wipe the top of the can with a clean towel or napkin before you puncture it.
• Measure the formula. Don't take shortcuts in measuring. If you're using powdered formula, fill the scoop provided and shave off any excess formula with the flat side of a knife. Don't use a spoon or any other curved surface. You can pour liquid concentrate directly into a bottle with ounce levels marked on its side, or you can use a measuring cup. Make sure that the quantity is level with the correct measurement mark.
• Mix the formula. Powdered and liquid concentrate formulas must be mixed with water. If you have any doubts about the safety of your drinking water, check with your local water utility or have your water tested. Use the exact amount of water the manufacturer specifies on the label. If the formula is too dilute or too concentrated, you may upset your baby's electrolyte balance and your baby's nutritional needs won't be met. Never dilute formula to make it last longer.
• Warm the formula, if needed. It's fine to give your baby room temperature or even cold formula. If your baby prefers warm formula, place a filled bottle in a bowl or pan of hot water and let it stand for a few minutes. Shake the bottle after warming it. Then turn it upside down and allow a drop or two of formula to fall on your wrist to test the temperature. It should be lukewarm — not hot. Don't warm bottles in the microwave. The formula may heat unevenly, creating hot spots that could burn your baby's mouth.
• Refrigerate extra bottles. If you prepare and fill several bottles at once, refrigerate the extra bottles until you need them. Discard any prepared formula that's been in the refrigerator more than 24 hours — or any formula that remains in the bottle after a feeding.

Fussing, crying and spitting up rarely indicate a baby's intolerance to infant formula. But a few babies don't respond well to certain formulas. Report any of these signs to your baby's doctor:

• Diarrhea
• Persistent or increasingly forceful vomiting
• Unusual fatigue or weakness
• Dry, red, scaly skin
• Gas

If your baby's doctor suspects a reaction to the formula you're using, he or she may suggest switching brands or trying another type of formula.