Alimentum vs. Nutramigen vs. PurAmino

If your pediatrician has recommended a hypoallergenic formula, your baby likely has confirmed or strongly suspected cow's milk protein allergy (CMPA). This affects approximately 2–3% of infants and typically presents with one or more of: blood in stool, persistent vomiting, failure to thrive, severe eczema, or chronic diarrhea.

This is not the same as mild fussiness or gas. CMPA is a medical condition that requires appropriate formula — not a gentle or sensitive formula, but a truly hypoallergenic one.

Alimentum and Nutramigen are the first-line hypoallergenic options. They use extensively hydrolyzed casein — cow's milk protein broken into fragments small enough that approximately 90% of CMPA babies can tolerate them. PurAmino goes further, using free amino acids instead of protein chains. It is for the roughly 10% of CMPA babies who react even to extensively hydrolyzed formulas, or babies with multiple food protein intolerances.

These formulas should be used under pediatric guidance. This guide helps you understand the differences, but your doctor should direct the decision.

For more on feeding amounts by age, see our baby feeding chart.

All three are designed for the same problem but at different levels of protein breakdown.

Extensively hydrolyzed vs. amino acid-based

Alimentum and Nutramigen use extensively hydrolyzed casein. The protein is broken into small peptides (protein fragments) that are too small to trigger an immune response in most allergic babies. About 90% of CMPA babies tolerate these formulas.

PurAmino uses free amino acids — the building blocks of protein, with no protein chains at all. This eliminates any possibility of protein-triggered immune response. It is reserved for babies who react to even the small peptides in extensively hydrolyzed formulas, or babies with multiple food protein intolerances (e.g., FPIES — food protein-induced enterocolitis syndrome).

LGG probiotic: Nutramigen's differentiator

Nutramigen includes LGG (Lactobacillus rhamnosus GG), a well-studied probiotic. Research suggests LGG may help some CMPA babies develop cow's milk tolerance faster. A study in the Journal of Allergy and Clinical Immunology found that infants receiving Nutramigen with LGG were more likely to acquire tolerance by 12 months compared to those on formula without LGG. This is a meaningful addition backed by evidence.

Fat source: MCT oil and palm olein

Alimentum and PurAmino include MCT oil (medium-chain triglycerides), which is easier to absorb — important for babies with compromised gut function from allergic inflammation. Nutramigen uses palm olein, which may contribute to firmer stools. For a baby already dealing with gastrointestinal inflammation from CMPA, the easier-absorbing fat blend in Alimentum may be an advantage.

Hypoallergenic formulas taste and smell significantly worse than standard formula. The hydrolysis process that breaks down proteins also produces bitter-tasting peptides. PurAmino, being amino acid-based, has the most distinctive taste and odor. Parents should be prepared for this — it is an unavoidable consequence of the formulation, not a defect.

Babies who start on hypoallergenic formula from birth typically accept the taste without issue. Older babies transitioning from standard formula may resist. Gradual transition over several days can help, but some babies need time to adjust.

Store-brand hypoallergenic formulas exist. Perrigo makes extensively hydrolyzed store-brand options (Parent's Choice Hypoallergenic, Up & Up Hypoallergenic) that cost 25–35% less than name brands. They meet the same FDA requirements. Ask your pediatrician if a store-brand option is appropriate for your baby.

Insurance coverage: some insurance plans and WIC programs cover hypoallergenic formula with a prescription or letter of medical necessity from your pediatrician. The cost difference ($200–380/month) makes this worth pursuing.

Taste and smell: All three have a strong, distinctive taste and odor. PurAmino is the most intense. This is normal and unavoidable.

Mixing: Alimentum and Nutramigen can be clumpy and benefit from vigorous shaking or a formula pitcher. PurAmino dissolves more easily. All may produce frothy bottles — let them settle before feeding.

Stool changes: Expect changes. Stools on hypoallergenic formula are often greenish, looser, and stronger-smelling. This is normal and expected — not a sign of intolerance.

Availability: Alimentum and Nutramigen are available at major retailers and pharmacies. PurAmino may need to be ordered online or through a pharmacy. Stock varies — keep a backup supply.

If your baby is on a hypoallergenic formula and symptoms persist or worsen, your pediatrician needs to know. This may indicate a need to escalate from extensively hydrolyzed (Alimentum/Nutramigen) to amino acid-based (PurAmino), or it may suggest a different diagnosis.

For most CMPA babies, Alimentum or Nutramigen will resolve symptoms. They are comparably priced and both extensively hydrolyzed. PurAmino is reserved for severe cases.

Choose Alimentum if: you want a palm-olein-free fat blend with MCT oil, or your baby has compromised gut absorption.

Choose Nutramigen if: the LGG probiotic for faster tolerance development appeals to you, or your baby's pediatrician specifically recommends it.

Choose PurAmino if: your baby does not improve on Alimentum or Nutramigen after 2–4 weeks, has multiple food protein intolerances, or has FPIES.

All three decisions should involve your pediatrician. CMPA management benefits from professional guidance and careful symptom tracking.

If you are trialing a hypoallergenic formula, tracking feeds, diapers, fussiness, and skin symptoms for 2–4 weeks gives your pediatrician the data needed to make informed decisions. tinylog makes this easy.

For gentle (non-hypoallergenic) options, see Similac Sensitive vs. Enfamil Gentlease. For the standard formula comparison, see Enfamil vs. Similac.

• Best Hypoallergenic Formulas — When you need one and how to choose
• Milk Protein Allergy in Poop — Signs of allergy in your baby's diaper
• Switching Formulas — How to do it safely

• U.S. Food and Drug Administration. "21 CFR Part 107 — Infant Formula." Code of Federal Regulations.
• American Academy of Pediatrics. "Choosing a Formula for a Baby with Cow's Milk Allergy." HealthyChildren.org, 2024.
• Canani RB, et al. "Formula selection for management of children with cow's milk allergy influences the rate of acquisition of tolerance." Journal of Allergy and Clinical Immunology, 2013.
• Koletzko S, et al. "Diagnostic approach and management of cow's-milk protein allergy." Journal of Pediatric Gastroenterology and Nutrition, 2012.
• Vandenplas Y, et al. "Guidelines for the diagnosis and management of cow's milk protein allergy in infants." Archives of Disease in Childhood, 2007.
• U.S. FDA. "Infant Formula Guidance Documents and Regulatory Information." fda.gov, 2023.

This guide is for informational purposes only and is not a substitute for professional medical advice. Hypoallergenic formula decisions should be made in consultation with your pediatrician. If you suspect your baby has a food allergy, seek professional evaluation.