Infeksi pada bayi masih menjadi masalah utama, terutama akibat imunitas yang belum matang. Bayi tanpa ASI eksklusif memiliki risiko diare lebih tinggi. Konsumsi susu formula meningkatkan risiko diare hingga 10,5 kali karena potensi kontaminasi dan ketiadaan komponen imunoprotektif ASI. Pada saat yang sama, promosi susu formula semakin masif dan berpotensi mempengaruhi pengetahuan, sikap, serta praktik ibu dalam pemberian makan bayi. Penelitian ini bertujuan untuk menggambarkan secara mendalam bagaimana ibu yang memiliki bayi di wilayah kerja Puskesmas Wonogiri memahami, menyikapi, dan mempraktikkan pemberian susu formula, serta menelaah pengaruh framing pesan iklan berdasarkan Teori Nudge. Penelitian menggunakan pendekatan kualitatif melalui wawancara mendalam dan observasi. Informan meliputi ibu dengan bayi usia kurang dari 6 bulan, kader kesehatan, bidan KIA, Dinas Kesehatan Wonogiri, anggota keluarga terdekat, serta pedagang susu formula.Hasil penelitian menunjukkan bahwa pengetahuan ibu tentang konsep susu formula umumnya baik, namun pemahaman mengenai kandungan serta perbedaan biologis antara susu formula dan ASI masih beragam. Media sosial, khususnya TikTok, menjadi sumber informasi utama yang membentuk persepsi awal ibu. Praktik pemberian makan bayi dipengaruhi oleh produksi ASI, kondisi medis ibu dan bayi, serta rekomendasi keluarga. Keluarga, terutama suami, ibu kandung, dan mertua, memiliki peran dominan dalam pengambilan keputusan penggunaan susu formula. Penyuluhan tenaga kesehatan turut mempengaruhi keputusan ibu, meskipun belum diterima secara merata. Dalam perspektif Teori Nudge, iklan lebih berfungsi sebagai pemicu perhatian dan pencarian informasi tambahan, sementara keputusan akhir lebih dipengaruhi oleh pengalaman sesama ibu dan dukungan keluarga. Temuan ini menegaskan bahwa pengaruh iklan bekerja melalui interaksi kompleks antara pesan komersial, dinamika keluarga, dan pengalaman menyusui ibu.

Infections remain a major health concern among infants, largely due to their immature immune systems. Infants who are not exclusively breastfed face a higher risk of diarrhea. Formula feeding increases the risk of diarrhea up to 10.5 times, due to potential contamination and the absence of natural immunoprotective components found in breast milk. At the same time, the promotion of infant formula has become more widespread and may influence mothers’ knowledge, attitudes, and practices in infant feeding. This study aims to explore in depth how mothers with infants in the working area of Wonogiri Primary Health Center understand, respond to, and practice formula feeding, as well as to examine the influence of advertising message framing based on Nudge Theory. A qualitative approach was used through in-depth interviews and observations. Informants included mothers with infants under six months old, health volunteers, maternal and child health midwives, the Wonogiri District Health Office, close family members, and infant formula sellers. The results show that mothers generally have good knowledge about infant formula, but their understanding of its nutritional content and biological differences compared to breast milk varies. Social media, especially TikTok, is the main source of information that shapes mothers’ initial perceptions. Infant feeding practices are influenced by breast milk production, medical conditions of the mother and baby, and family recommendations. Family members—especially husbands, biological mothers, and mothers-in-law—play a major role in decisions about using infant formula. Health education from health workers also affects mothers’ decisions, although it is not equally received by all mothers. From a Nudge Theory perspective, advertisements mainly act as attention triggers and encourage further information seeking, while final decisions are more strongly influenced by other mothers’ experiences and family support. These findings show that the influence of advertising works through a complex interaction between commercial messages, family dynamics, and mothers’ breastfeeding experiences.