Romans 1:24

Wherefore God also gave them up to uncleanness
Not by putting any into them, but by leaving them to the pollution of their nature; by withdrawing his providential restraints from them, and by giving them up to judicial hardness:

through the lusts of their own hearts.
The heart of man is the source of all wickedness; the lusts that dwell there are many, and these tend to uncleanness of one sort or another: by it here is meant particularly bodily uncleanness, since it is said they were given up

to dishonour their own bodies between themselves;
either alone, or with others; so that as they changed the glory of God, and dishonoured him, he left them to dishonour themselves by doing these things which were reproachful and scandalous to human nature.