alterar
verbCEFR B2
What does “alterar” mean in English?
to alter, to disrupt
to alter, to disrupt (to change or disturb, often implying negative or unwanted change)
Example sentences
El temporal ha alterado gravemente el tráfico en las principales vías de comunicación de la región.
The storm has severely disrupted traffic on the main communication routes in the region.
La revelación de los documentos secretos alteró radicalmente la percepción pública del caso.
The revelation of the secret documents radically altered public perception of the case.
El detective advirtió que alguien había alterado las pruebas antes de que llegaran los peritos.
The detective warned that someone had tampered with the evidence before the experts arrived.
How to use it
Alterar means 'to alter', 'to change', or 'to modify' something. It often implies unwanted or significant change: alterar el orden público (disturb public order), alterar los resultados (tamper with results). The reflexive alterarse means 'to become upset' or 'to be disturbed': no te alteres (don't get upset / don't lose your composure). At B2, both the transitive (altering something) and the reflexive emotional sense are important. Key distinction from modificar: alterar suggests more disruptive or worrying change.
Common mistake
Alterar (disrupt/tamper with) has a more negative connotation than modificar (neutral modification) or ajustar (fine-tuning). English 'alter' maps closest to alterar, but 'tamper with' is a better translation when alterar implies improper interference (alterar pruebas, alterar datos). The reflexive alterarse (to get upset) is a separate and common meaning: 'se alteró cuando le dieron la noticia' — 'she became upset when they gave her the news'.