Formula feeding: preparation and safety

Age: Newborn · Category: Feeding

Whether you have chosen formula from the start, are supplementing breastfeeding or have moved to formula after breastfeeding, you are giving your baby a nutritious and safe way to grow. Infant formula is regulated to meet strict nutritional standards, and when it is prepared and stored correctly it provides everything your newborn needs in the early months. This guide covers how to choose the right type, how to prepare and store it safely, how much to offer at each stage, and how to recognise and respond to common concerns.

Choosing the right type of formula

The vast majority of healthy full-term babies do well on standard infant formula made from modified cow's milk protein. These formulas are designed to mimic the composition of breast milk as closely as possible, adjusting the ratio of whey to casein protein, reducing saturated fat and adding vitamins and minerals such as iron, vitamin D, iodine and omega-3 fatty acids. Look for products labelled "Stage 1" or "First infant formula", which are suitable from birth and throughout the first year.

Follow-on formula is marketed for babies over six months old. According to the NHS, follow-on formula is not necessary and a healthy baby can continue on first infant formula past six months. Follow-on products should never be given to babies under six months.

Hypoallergenic formulas fall into two broad categories. Extensively hydrolysed formulas (eHF) contain cow's milk protein that has been broken into smaller fragments, making it less likely to trigger an immune response. Amino-acid-based formulas (AAF) contain no intact proteins at all and are used for the most severe cases of cow's milk protein allergy (CMPA). The AAP and NHS both advise that these formulas should only be used under medical guidance, as a diagnosis of CMPA needs to be confirmed before switching.

Soya-based formula and goat's milk formula are also available. Neither is recommended as a first choice by the WHO, AAP or NHS. Soya formula contains phytoestrogens and is not suitable for babies under six months. Goat's milk formula does not offer a meaningful advantage over cow's milk formula and is not appropriate for babies with confirmed cow's milk protein allergy because the proteins are structurally similar.

How to prepare formula safely

Safe preparation is critical because powdered infant formula is not a sterile product. Harmful bacteria including Cronobacter sakazakii can occasionally be present in the powder, and a newborn's immune system is not yet equipped to fight such infections. The following steps are based on guidance from the WHO and NHS.

Sterilising equipment

Before each feed, sterilise all bottles, teats, caps and rings. You can use a cold-water sterilising solution, a steam steriliser (electric or microwave) or boiling. If boiling, submerge all items in a large pan of water, bring to the boil and keep boiling for at least 10 minutes. Remove with sterile tongs. Wash your hands thoroughly with soap and water before handling sterilised equipment and before making up a feed.

Water temperature

The WHO and NHS recommend making up feeds with water that has been boiled in a kettle and then allowed to cool to no lower than 70 degrees C (158 degrees F). This temperature is hot enough to kill most bacteria in the powder. Do not use water from a water softener, artificially mineral-enriched water, or water that has been boiled multiple times. If you are using bottled water, check the label to ensure sodium (Na) content is below 200 mg per litre and sulphate (SO4 or SO4) is below 250 mg per litre, and still boil it before use.

Measuring and mixing

Pour the correct amount of hot water into the sterilised bottle first, then add the powder. Always use the scoop provided with that specific brand and level off each scoop with a clean, dry knife or the leveller built into the tin. Never add extra scoops to make feeds more concentrated, and never add fewer scoops to make them more dilute. Both practices are dangerous: an over-concentrated formula can overload your baby's kidneys and cause serious harm; an under-concentrated formula will not provide adequate nutrition. Shake the bottle firmly until the powder is fully dissolved, then cool rapidly under cold running water or in a bowl of iced water. Test the temperature by shaking a few drops on your inner wrist before feeding.

Storing formula correctly

Freshly made formula can be kept in the back of a refrigerator (5 degrees C or below, not in the door) for a maximum of 24 hours. Never freeze formula. If you are going out, you can carry a made-up feed in a cool bag with an ice pack for up to four hours, or carry the powder and cooled boiled water separately and combine them when needed.

Once your baby has started drinking from a bottle, saliva from the teat can introduce bacteria into the remaining formula. Any formula left in the bottle after a feed must be discarded within two hours, even if it has been refrigerated. Never save a part-used bottle for the next feed.

Ready-to-feed (RTF) liquid formula is sterile until opened and is a useful option when you are away from home or in the early days when you are exhausted. Once opened, follow the manufacturer's instructions, but most require refrigeration and use within 24 hours.

How much formula to offer and when

Newborn stomachs are tiny and feeds are frequent. In the first few days, most babies take only 30 to 60 ml (1 to 2 oz) per feed every 2 to 3 hours. By the end of the first month, this typically rises to 90 to 120 ml (3 to 4 oz) per feed, still roughly every 3 hours. By three months, feeds may increase to 150 to 180 ml (5 to 6 oz) every 3 to 4 hours.

A commonly cited guide from the AAP is approximately 70 to 100 ml of formula per kilogram of body weight per day. For example, a baby weighing 4 kg might take between 280 and 400 ml across the whole day, spread over 6 to 8 feeds. These are averages: healthy babies have varying appetites day to day and will naturally take more during growth spurts.

Hunger cues

Crying is a late hunger signal. Earlier cues include turning the head from side to side (rooting), bringing hands to the mouth, sucking on fingers or fists, opening the mouth and sticking out the tongue, and becoming more alert and active. Responding to early cues leads to calmer feeds because your baby has not yet worked themselves into distress.

Fullness cues

Signs that your baby has had enough include turning the head away from the teat, closing the lips, falling asleep at the bottle, becoming distracted or pushing the bottle away. The CDC advises parents not to encourage babies to finish a bottle once they show fullness cues, because doing so can lead to overfeeding and may disrupt the baby's ability to regulate their own appetite later in life.

Common concerns and when to act

Constipation

Formula-fed babies typically poo less often than breastfed babies, and their stools are firmer and darker. Some constipation is normal in the early weeks. A baby who is straining but passes a soft stool is not constipated. True constipation means hard, pellet-like stools and significant discomfort. If this is persistent, speak to your health visitor or doctor. Never add anything to formula, including extra water, sugar or fruit juice, without medical advice.

Wind and reflux

Swallowing air during bottle feeds can cause discomfort and spitting up. Winding your baby mid-feed and at the end of each feed, using a slow-flow teat, and keeping your baby semi-upright for 20 to 30 minutes after a feed can all help. Posseting (small amounts of milk brought up after a feed) is extremely common and usually harmless. If your baby is bringing up large amounts repeatedly, seems to be in pain, or is not gaining weight well, speak to a doctor, who may consider anti-reflux measures or, in some cases, anti-reflux formula.

Possible allergy

Cow's milk protein allergy (CMPA) affects roughly 2 to 3 percent of formula-fed babies according to the AAP. Symptoms can include persistent eczema, blood or mucus in stools, vomiting, diarrhoea, or signs of respiratory distress. These symptoms can overlap with many other conditions, so a diagnosis should always be confirmed by a doctor before switching formula. Switching formulas without guidance can mask symptoms and delay accurate diagnosis.

Mixing formula incorrectly

Using too little powder (under-dilution) deprives your baby of essential nutrients and calories. Using too much powder (over-concentration) increases the load on immature kidneys and can cause hypernatraemia (raised blood sodium), a potentially serious condition. Always follow the manufacturer's instructions exactly, using only the scoop provided with that tin. If you are ever unsure, re-read the preparation instructions on the packaging before making up the next feed.

Frequently asked questions

How much formula does a newborn need in the first weeks?

In the first few days, most newborns take only 30 to 60 ml (1 to 2 oz) per feed, every 2 to 3 hours. By the end of the first month, this typically increases to 90 to 120 ml (3 to 4 oz) per feed. A general guide from the AAP is approximately 70 to 100 ml of formula per kilogram of body weight per day, though every baby's appetite varies. Always follow your baby's hunger and fullness cues rather than insisting they finish a bottle.

Can I make up formula feeds in advance and store them?

Yes, but with strict time limits. The WHO and NHS recommend making up feeds fresh when possible. If you need to prepare in advance, freshly made formula can be stored in the back of a refrigerator (at 5 degrees C or below) for no longer than 24 hours. Pre-made feeds should never be left at room temperature for more than 2 hours. Discard any formula left in the bottle after a feed because the baby's saliva can introduce bacteria.

What water temperature should I use to make up infant formula?

The WHO and NHS advise using water that has been boiled and then cooled to no lower than 70 degrees C (158 degrees F). Water at this temperature kills Cronobacter sakazakii and other harmful bacteria that can occasionally be present in powdered formula. Pour the hot water into the sterilised bottle first, add the correct number of scoops of powder, shake to dissolve, then cool rapidly under cold running water or in a bowl of iced water before feeding. Test the temperature on your wrist before giving it to your baby.

My baby seems gassy and uncomfortable after formula feeds. What can I do?

Wind after formula feeds is common because babies often swallow air while bottle-feeding. Pause mid-feed to wind your baby by holding them upright over your shoulder or sitting them upright on your lap and gently rubbing their back. Using a slow-flow teat and ensuring the teat is always full of formula rather than air can also help. If wind is persistent or your baby seems to be in significant pain, speak to your doctor or health visitor, who may consider a different formula or investigate other causes.

When should I consider switching to a different type of infant formula?

Most babies do well on standard cow's milk-based formula throughout the first year. You should only switch formulas on the advice of a doctor or dietitian. Signs that might prompt a review include persistent blood or mucus in the stool, persistent vomiting, a rash, wheezing or signs of significant distress after feeds that do not improve with winding techniques. If cow's milk protein allergy is suspected, a doctor may prescribe an extensively hydrolysed or amino-acid-based formula. Avoid switching formulas frequently without clinical guidance, as each change can temporarily upset your baby's digestion.

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