Types of Infant Formula

The one that is the default

First infant formula, often labelled first milk, is suitable from birth and is the only formula most babies ever need. The NHS is unusually direct about this: "unless a midwife, health visitor or GP suggests otherwise, first infant formula is the only formula your baby needs", and your baby can stay on it when solid food starts at around six months and drink it throughout the first year.

The reason is protein. Cows' milk contains whey and casein. First infant formula is based on whey, which is thought to be easier for a young baby to digest. Everything else on the shelf is a variation on that theme, and most of the variations are not improvements.

All infant formula sold in the UK must meet the same compositional standards, which is why the NHS states that "it does not matter if you choose a cheaper or more expensive brand of formula". In the United States the equivalent guarantee comes from the FDA, which requires infant formula to contain 30 specified nutrients.

The three physical forms

Formula comes as powder or as ready-to-feed liquid, and in the US also as a liquid concentrate that you dilute. Powder is the cheapest and the most common. Ready-to-feed is sterile in the carton, which makes it the safest option when you cannot boil water reliably, but it costs more and must be used quickly once opened. Powdered formula is not sterile, and that single fact drives almost all the preparation rules.

The ones with claims and no evidence

Hungrier baby formula

Hungry milk contains more casein than whey. Casein is harder for a baby to digest, which is the mechanism behind the marketing idea that it keeps babies fuller for longer. The NHS states there is "no evidence that babies settle better or sleep longer when fed this type of formula". It is suitable from birth, but ask a midwife or health visitor first.

Comfort formula

Comfort formula contains cows' milk protein that has been partly broken down, or partially hydrolysed. The claim is easier digestion and less colic and constipation. The NHS position is that "there's no evidence for this". Critically, partial hydrolysis is not enough for a baby with a diagnosed cows' milk allergy, and comfort formula is not suitable for them.

Goodnight milk

Goodnight milks are not suitable under six months and, in the NHS's assessment, are not needed after that either, with no evidence that babies settle better or sleep longer on them.

Follow-on formula and toddler milks

Follow-on formula must never be given under six months. Research shows switching to it at six months has no benefit, and your baby can stay on first infant formula until they are one. The labels look deliberately similar to first milk, so read them carefully. Growing-up and toddler milks are not needed at all once your child is twelve months old and can drink cows' milk. The AAP is blunter still, calling the names of these products "misleading" and noting they often carry added sugar, salt and protein and unproven health claims.

The ones that need a professional first

Anti-reflux, or staydown, formula

This is thickened formula intended to reduce how much milk comes back up. It is sold openly in pharmacies and supermarkets, but the NHS recommends using it only on the advice of a health professional, partly because the mixing instructions can differ from standard formula in a way that matters for safety.

Lactose-free formula

Suitable from birth but only under medical supervision. It is intended for babies who cannot absorb lactose. The NHS notes flatly that lactose intolerance is rare in babies, so a suspicion of it is a reason to see a GP rather than a reason to change tins.

Hypoallergenic formula

If a baby is diagnosed with cows' milk allergy, a GP will prescribe a formula with fully hydrolysed, extensively broken-down proteins. The AAP describes these as "predigested". They are different products from comfort formula, and the distinction is the whole point.

Soya formula

Suitable from six months and only under medical supervision. The NHS sets out the reason carefully: soya contains phytoestrogens, plant compounds whose chemical structure resembles oestrogen, and a baby's low body weight means their intake relative to size is far higher than an adult's. Soya formula is also more likely than cows' milk formula to harm teeth.

Goats' milk formula

Goats' milk formula is suitable from birth and is produced to the same nutritional standards as cows' milk formula. What it is not is an allergy solution. Both the NHS and the AAP say the same thing for the same reason: the proteins are very similar, cross-reactivity rates are high, and goats' milk formula is not suitable for a baby with cows' milk protein allergy.

Iron, and why low-iron formula is not a thing

Nearly all infant formula is iron-fortified, and the AAP recommends iron-fortified formula for every baby who is not breastfed or is only partly breastfed, from birth to one year. It states directly that "low-iron formulas should not be used", and that the amount of iron in infant formula does not cause constipation, despite the persistent belief that it does.

What never belongs in the bottle

Homemade formula is not a safe substitute; the AAP has a standing warning against it. Nor should anything be added to a made-up feed. The NHS is explicit that sugar and cereals do not go into formula, and that a bottle or trainer cup should contain nothing but breast milk, formula or water.

When to change anything

If you think a formula disagrees with your baby, the NHS asks you to talk to a midwife or health visitor rather than switching on your own, and notes there is "no evidence that switching to a different formula does any good or harm". Suspected allergy or intolerance is a GP conversation, because a prescribed formula may be needed.