What causes it

Raising Children Network names the main cause without hedging: "The main cause of nappy rash is wearing a wet or dirty nappy for too long." Skin is irritated by ammonia in wee and poo, and by the dampness itself.

The NHS lists the full set of causes: skin in contact with wee or poo for a long time, not cleaning or changing the nappy often enough, the nappy rubbing against the skin, an allergic reaction to soap, detergent or bubble bath, irritation from fragranced wipes or wipes containing alcohol, some medicines such as antibiotics or laxatives, and thrush.

Raising Children Network adds three specifics worth knowing: plastic pants stop air circulating and keep the area damp; some disposable wipes contain a chemical called methylisothiazolinone that can cause a reaction; and nappy rash "is less common in babies who are breastfed, because their poo is less irritating", and more common in babies in cloth nappies, which are less breathable and absorb less.

What it looks like

The NHS symptom list:

Red or raw patches on the bottom or the whole nappy area.
Skin that looks sore and feels hot to touch.
Scaly and dry skin.
An itchy or painful bottom.
Your baby seeming uncomfortable or distressed.
Spots, pimples or blisters — which "can appear red or brown, but may be less noticeable on brown and black skin."

Raising Children Network adds the same point about skin tone: inflammation "might look brown, purple or grey" on dark skin and "red" on light skin. It also notes that skin folds are not usually affected, because wee does not get into them — which is a useful diagnostic clue, because thrush does affect the folds.

What actually clears it

The goal, in Raising Children Network's words, is "to repair the damaged and irritated skin and protect it from any dampness and friction that might cause more damage." Four things do the work.

1. Change nappies far more often

The NHS: change wet or dirty nappies as soon as possible. Raising Children Network suggests checking every hour or so. The HSE gives useful baselines: young babies may need changing up to 10 or 12 times a day; older babies around 6 to 8 times. Change after every feed and as soon as possible after a poo — but there is no need to wake a sleeping baby to change them.

2. Clean gently, dry thoroughly

The HSE: "Use cotton wool and water to clean your baby's skin. Try not to use baby wipes until your baby is 2 to 4 weeks old." Gently wash and pat dry at each change. The NHS says to keep the skin clean and dry and to pat or rub gently, and that you can clean with water or with fragrance-free and alcohol-free baby wipes.

3. Barrier cream, applied properly

This is the step most people get wrong. Raising Children Network: "Apply a simple, cheap barrier cream at every nappy change. You could use a zinc cream or a petroleum jelly like Vaseline... You should apply the cream thickly enough to create a barrier that stops wee and poo from getting onto the skin. You'll know you're putting the cream on thickly enough if you can still see some of the cream at the next nappy change."

The NHS's pharmacist advice is the same: a thin layer of a barrier cream to protect the skin. Expensive is not better; coverage is.

4. Nappy-free time

The HSE: "Leave off the nappy for half an hour and expose the skin to fresh air, as much as possible." Raising Children Network: air the bottom for as long as possible every day, with a towel underneath. The NHS simply says to leave nappies off when possible.

Other things that help

Use extra-absorbent nappies and make sure they fit properly (NHS).
Consider switching temporarily to disposables if you normally use cloth, because they absorb more moisture (Raising Children Network).
Fasten the nappy loosely or use a larger size, to reduce friction and let air circulate.
Bath daily but not more than twice a day — the NHS notes that washing too much dries the skin out.
Give evening fluids earlier. Both the HSE and Raising Children Network suggest this so the overnight nappy is less wet.

What makes it worse

The NHS's "do not" list:

Do not use soaps, baby lotion or bubble bath — they can irritate the skin.
Do not use talcum powder or antiseptics on nappy rash.
Do not put nappies on too tightly, as it can irritate the skin.

The HSE adds: no bubble baths, talcum powder or any scented products. And one instruction that should not need saying but evidently does: "Never apply raw egg or any other food directly to broken skin."

Pain relief

The NHS notes a pharmacist may suggest infant paracetamol for pain relief — but with a specific age limit: it is only suitable for babies over 2 months old. Do not give paracetamol to a younger baby unless a doctor has prescribed it.

When it is not just nappy rash

If the rash does not clear within a few days, there may be an underlying infection. Raising Children Network describes thrush as "bright, inflamed patches with clearly defined borders in the nappy area", often with "a lot of dots or pus-filled bumps (pustules) beyond the outer edge of the rash", and notes that thrush can affect the skin folds — unlike ordinary nappy rash. Thrush needs a prescribed antifungal cream and often takes longer to clear, and can come back.

A GP may prescribe a steroid cream or ointment for redness and soreness, an antifungal cream for thrush, or antibiotics for a bacterial infection (NHS). Raising Children Network notes weak corticosteroids such as hydrocortisone 1% are safe for short periods under a doctor's supervision.

When to call

See a health visitor or GP if:

The nappy rash does not go away, gets worse, or spreads to other areas (NHS) — Raising Children Network's threshold is no improvement after a week of the treatment above.
Your baby has a high temperature, or an unexplained fever.
Your baby seems very uncomfortable, is upset and is not sleeping.
There are blisters, crusts or pimples.
There is inflammation, swelling or a scab at the end of the penis.

Contact your GP if your baby also has severe pain and distress when pooing, blood in their poo, fever, vomiting, constipation, bloody diarrhoea, a bloated tummy or low energy — the HSE lists these separately, because a rash plus those symptoms is a different conversation.

Raising Children Network makes one final point in favour of treating it promptly rather than waiting it out: nappy rash "increases the risk of urinary tract infection and vaginal infections in girls. This is why it's important to treat nappy rash and prevent it if you can."

Nappy Rash