Few first-year decisions get more conflicting advice than when to start solids. A pediatrician says four months. A relative says six. A friend’s app says “around five.” The frustrating part is that all three are pointing at real guidance — they just weight different parts of it.

Here is what the major pediatric bodies actually say, and what it means for the decision in your house.

Where the two numbers come from

The World Health Organization recommends exclusive breastfeeding for the first six months, then introducing complementary foods. The WHO position is built around global maternal and infant health, including settings where water safety, food hygiene, and breast-milk substitutes are not guaranteed.

The American Academy of Pediatrics, in line with the US Dietary Guidelines, recommends introducing complementary foods at around six months, but allows that some infants may be ready earlier — not before four months. The AAP and the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) both define the window as 4 to 6 months for healthy, term infants showing readiness signs.

These two positions are not in disagreement. The WHO sets a public-health floor; the AAP sets an individual-readiness window. Both agree that food before 4 months is too early. Both agree that 6 months is a reasonable target for most infants.

The signals that matter more than the number

Pediatricians look at readiness, not just age:

Steady head and neck control. The baby can sit upright (with some support) without flopping.
Loss of the tongue-thrust reflex. Spoon contents go in rather than out.
Active interest in food. Watching the family eat, opening the mouth, reaching for what’s on the plate.
Ability to move food from front to back of the mouth. Without this, food just sits and frustrates.
Doubled birth weight, generally above 13 lb (~6 kg).

A baby showing all five at five months is ready. A baby showing none at six months is not. The age is a guide; the readiness signs are the decision.

Why the WHO and AAP weight the question differently

The 6-month target is grounded in three things:

Gut maturity. The infant intestine develops the capacity to handle non-milk proteins gradually over the first half-year. Earlier exposure is not necessarily harmful, but the digestive system is not yet at its full capacity to absorb iron and zinc from food.
Nutritional adequacy of breast milk. For full-term infants of well-nourished mothers, breast milk meets nutritional needs through approximately six months. Iron stores from birth start to deplete around that point — which is why iron-rich complementary foods then become important.
Reduced infection risk. Exclusively breastfed infants have measurably lower rates of respiratory and gastrointestinal infection in the first six months.

The AAP’s earlier flexibility comes from clinical reality:

Some infants need more. Formula-fed infants, infants with growth concerns, or infants whose mothers cannot continue exclusive breastfeeding may benefit from earlier complementary foods.
Allergen introduction windows. Recent allergy research — particularly the LEAP study on early peanut introduction — has moved consensus toward introducing common allergens between 4 and 6 months in higher-risk infants. Waiting too long can raise allergy risk, not lower it.

Both positions are correct for their target. The question is which one applies to your baby.

What to introduce first

There is no single mandated first food. What the evidence supports:

Iron-rich foods are the priority. Iron-fortified cereal, pureed meats, or well-mashed lentils.
Texture matters as much as ingredients. Smooth purees first, then thicker textures, then soft pieces. The progression should happen over weeks, not months, to support oral-motor development.
Introduce common allergens deliberately. The LEAP study and follow-up research have shifted consensus: introducing peanut, egg, dairy, wheat, soy, fish, and tree nuts in age-appropriate forms between 4 and 11 months may reduce the risk of food allergy, particularly in higher-risk infants.

For families with a strong allergy history, talk to a pediatrician before introducing peanut or egg — a supervised first exposure is sometimes appropriate.

What not to do

No honey before 12 months. Infant botulism is rare but serious.
No cow’s milk as the main drink before 12 months. Small amounts in cooking are fine.
No salt, no added sugar. Infant kidneys are not equipped for added salt, and added sugar at this age sets sweet-preference patterns that are hard to reverse.
No choking-shape foods. Whole grapes, whole nuts, hot-dog rounds, hard candy, popcorn. The hazard category is texture and shape, not the food itself.

A reasonable framework

Most parents are well served by this sequence:

Watch for readiness signs starting at four months. Do not start before four months unless a pediatrician advises it.
Introduce a single iron-rich food at around six months — earlier if readiness is clear and there is medical reason to start earlier.
Move through texture progression over the following 4–6 weeks: thin puree → thicker puree → mash → soft finger food.
Introduce common allergens during this window deliberately, one at a time.
Keep breast milk or iron-fortified formula as the primary nutrition source until 12 months; complementary foods are complementary, not yet primary.

The 4-vs-6-month debate is less a disagreement than a choice of frame. WHO is right about the population. The AAP is right about the individual. Your job is to look at the baby in front of you.

References

American Academy of Pediatrics, Committee on Nutrition. Complementary Feeding. Pediatrics.
World Health Organization. Infant and young child feeding: Model Chapter for textbooks for medical students and allied health professionals.
Du Toit G, Roberts G, Sayre PH, et al. Randomized trial of peanut consumption in infants at risk for peanut allergy (LEAP). New England Journal of Medicine.
American Academy of Pediatrics. Bright Futures: Guidelines for Health Supervision of Infants, Children, and Adolescents.
European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN). Complementary Feeding: A Position Paper.