Saúde vs. santinho
Both saúde and santinho are used to say "bless you" after a sneeze, but they differ significantly in geographical usage and literal meaning. While one focuses on physical well-being and is universal, the other is cultural and specific to Portugal.
Saúde
A1This is the standard word for "bless you" in Brazil and is also widely used in Portugal. It literally translates to "health," expressing a wish for the sneezer to remain healthy.
Sempre dizemos saúde quando alguém espirra na sala de aula.
(We always say bless you when someone sneezes in the classroom.)
Saúde! Você precisa de um lenço?
(Bless you! Do you need a tissue?)
Ele espirrou três vezes e eu disse saúde três vezes.
(He sneezed three times and I said bless you three times.)
É educado dizer saúde após um espirro no escritório.
(It is polite to say bless you after a sneeze in the office.)
Desejo muita saúde para você.
(I wish much health to you.)
Santinho
B1This word is used primarily in Portugal to say "bless you" and is extremely rare in Brazil. It literally means "little saint" and implies that the sneeze expelled a demon, leaving the person pure like a saint.
A avó portuguesa sempre diz santinho aos netos.
(The Portuguese grandmother always says bless you to her grandchildren.)
Santinho! Está muito frio aqui fora.
(Bless you! It is very cold out here.)
Em Portugal, é comum ouvir santinho na rua.
(In Portugal, it is common to hear bless you on the street.)
O padre sorriu e disse santinho.
(The priest smiled and said bless you.)
Santinho, e que Deus te ajude.
(Bless you, and may God help you.)
Summary
Use saúde in any Portuguese-speaking country, especially Brazil, as it is the neutral and universal wish for good health. Use santinho specifically in Portugal if you want to sound local or affectionate, particularly in informal settings.