This study is a prospective, multicenter, randomized controlled trial designed to evaluate the clinical efficacy, tolerance, and safety of a partially hydrolyzed whey protein formula in infants with mild allergic symptoms. Partially hydrolyzed formulas contain low-molecular weight peptides and have been shown to improve protein tolerance and digestibility and to reduce allergenicity compared with intact cow's milk protein formulas. However, evidence regarding their therapeutic effects in infants who have already developed allergic symptoms remains limited.

Eligible infants with mild allergic manifestations who are predominantly formula-fed will be randomly assigned in a 1:1 ratio to receive either a partially hydrolyzed whey protein formula or an intact cow's milk protein formula. Infants in the intervention group will receive a 100% partially hydrolyzed whey protein formula during the initial intervention period and will transition to a 60% partially hydrolyzed whey protein formula after reaching 6 months of age, while infants in the control group will continue feeding with an intact protein formula.

The primary outcome is the overall improvement rate of allergic symptoms after 2 weeks of intervention. Secondary outcomes include tolerance after transition to the follow-on formula at 6 months of age, changes in skin, gastrointestinal, and respiratory symptoms, growth parameters, and safety outcomes. The results of this study are expected to provide evidence to support nutritional management strategies for infants with mild allergic symptoms.

Inclusion Criteria:

1. Infants aged ≥12 weeks and <20 weeks at the time of screening.
2. Gestational age ≥37 weeks.
3. Birth weight ≥2500g.
4. Presence of mild allergic symptoms (e.g., skin, gastrointestinal, or respiratory symptoms).
5. Infants who are predominantly formula-fed or mixed-fed at the time of enrollment.
6. Legal guardian has provided written informed consent and agrees to participate in the study.

Exclusion Criteria:

1. Diagnosed with moderate or severe food allergies, including a history of allergic conditions such as atopic dermatitis, wheezing bronchitis, or severe allergic reactions.
2. Confirmed cow's milk protein allergy.
3. Currently receiving a partially hydrolyzed formula or any other specialized formula.
4. Exclusively breastfed infants.
5. Known allergy or intolerance to the study formula.
6. Presence of severe illness (e.g., digestive, respiratory, neurological infections, other gastrointestinal diseases, gastrointestinal anatomical abnormalities, congenital malformations, or growth retardation).
7. Infants with a history of severe diseases such as heart, brain, liver, kidney, hematologic, connective tissue, endocrine diseases, or mental disorders.
8. Infants who have undergone major surgery that may impact the study outcomes.
9. Infants who have used systemic immune-modulating medications (e.g., anti-allergy drugs, corticosteroids, immunosuppressants, biological agents) within the last 2 weeks.
10. Infants who have used gastrointestinal medications (e.g., proton pump inhibitors, gastrointestinal motility agents, or digestive remedies) within the last 7 days.
11. Infants who have used probiotics within the last 7 days.
12. Parents who are unable to report the occurrence of symptoms or adhere to the study visits and protocol requirements.