Sibling estrangement or sibling alienation is the breakdown of relationships between siblings resulting in a lack of communication or outright avoidance of each other. It is a phenomenon that can occur in families for various reasons such as unresolved conflicts, personality differences, distance, or life events. Similar to family estrangement, sibling estrangement is also linked to disruptive family events, such as parental divorce or the death of a family member. It includes emotional and physical distancing of siblings. It is a voluntary and intentional process in which at least one sibling creates or keeps distance from another sibling, triggered by a negative relationship between them. It can happen at different ages, in the majority of cases it happens during adulthood.

Sibling alienation can be significantly influenced by childhood dynamics, such as sibling rivalry and parental favouritism. Siblings who experienced a lot of rivalry, resentment, and conflict as children are more likely to have strained relationships as adults. Parental favouritism can exacerbate this by causing resentment and escalating sibling conflict.

Sibling estrangement can result from personality differences, attachment styles, communication preferences, and life experiences, among other personal distinctions. Some personality characteristics, such as neuroticism or extraversion, make people more or less likely to experience sibling estrangement. Attachment theory suggests that early interactions with caregivers can shape a person's attachment style, which in turn can have an impact on their adult relationships. Individuals with insecure attachment patterns are more likely to experience alienation from their siblings in the context of sibling estrangement. Sibling relationships can be impacted by differences in communication methods, such as conflict resolution techniques or the ability to reveal personal information. Personality conflicts can result in disagreement, which is a frequent cause of estrangement.

Sibling estrangement can be significantly influenced by life events. An individual's capacity to sustain relationships with their siblings can be affected by a variety of circumstances, including the death of a parent or sibling, traumatic or abusive events, and mental health problems. For instance, a sibling who has experienced abuse may find it difficult to trust them or feel secure in their presence, which might result in alienation. The incidence and length of estrangement can be influenced by the seriousness and timing of these occurrences. Life events are just one of several factors that can contribute to sibling estrangement, and their precise role may vary depending on the specific circumstances of each case.

Effective communication is essential for maintaining healthy sibling relationships. Poor communication, misunderstandings, and conflicts in communication styles can create barriers that make it difficult for siblings to connect and maintain a strong bond. In some cases, siblings may even avoid communication altogether, leading to a breakdown in their relationship. The importance of communication in sibling relationships makes it possible for estrangement to develop.

Any form of sexual, emotional, or physical abuse that takes place between siblings is referred to as sibling abuse. This can involve destructive actions such as bullying, physical aggression, and verbal abuse. The impacts of sibling abuse can endure a lifetime for those affected, increasing their vulnerability to mental health disorders and interpersonal interaction troubles.

Mental health and substance abuse can contribute to sibling estrangement in different ways. For instance, one sibling may keep their distance from a sibling who is battling addiction or mental illness. Some individuals may use estrangement as a way of coping with their own mental health or substance use issues. This could be brought on by the strain of handling the circumstance or worries about how it will affect other family members. Mental health issues could also affect the ability of siblings to communicate effectively, leading to misunderstandings and conflicts that can drive them apart. Sibling estrangement itself can be challenging and lead to eventual problems with mental health and substance abuse.

Genetic relatedness has been established as a significant risk factor, despite the impact of childhood co-residence having a large impact on its significance. Full siblings are less likely to experience estrangement than half and step-siblings who lived together for at least half of their upbringing. Non-biological siblings who had little to no history of childhood co-residence are more likely than other siblings to become estranged from one another.