Is it a sin to wear makeup? I recall reading a Saint saying that women wearing heavy makeup is a sin as it's deceptive. I personally don't think women should wear makeup and heavy makeup is indeed fraudulent.

I don't remember the saint who said it. 

There was a huge thread on the subject.  Linked above is a more recent revisitation of the question, but there was a thread some years ago that went on for an extremely long time.

It was one or another of the Church Fathers who denounced make up on account of "deception", but I suspect that it had to do with heavier amounts of make up.  With the lighter amounts of makeup, there's a very fine line between what qualifies more as grooming and/or just covering up something that might be unsightly.  If I had an open wound on my face, even if it wasn't infectious or messy, but just kindof gross, it wouldn't be "deception" in any kind of formal sense, just to cover it up.  But then what if you have some acne or splotchy skin ... there's a gray line between not being unsighly and trying to be attractive.

But then what if I put on nice clothes, a nice suit, or a nice dress.  Isn't that intended to create a sense of dignity for your "temple of the Holy Ghost", as St. Paul says about dressing?  So, is putting in a bit of make up to look a bit nicer or more dignified, less gross, less like you just rolled out of bed.  Is coming your hair or putting in some hair spray or styling gel, is that deception, or is it an attempt to look "nice", or civilized.  How about shaving?  Isn't that "deceptive", since the natural state of a man would be to have facial hair?

Bottom line is that there's a fine line between just trying to make yourself look presentable, civilized, etc. and attempting to deceive, such as if an unmarried young lady significantly altered her appearance to the point that she didn't really look like herself, but some other person.

There's a story about St. Therese where she famously did up her hair, put some earrings in, etc. ... to make herself seem older, since she was trying to get permission to enter the convent at a younger age than was normally permitted.  That was a type of "deception", in a way, right?

But if you think about the formal notion of deception, it has to do with defrauding someone of the truth ... IF the individual has a right to it.  Not every random person has a right to know everything about you.  Does a random person on the street have some kind of right to know that you have some skin problem or some acne, or to see every single blemish on your skin?  Of course not.  So not sharing that information with them ... by covering up with makeup, how is that different from not sharing information about yourself by, say, putting on long-sleeve shirt if you have some skin condition on your arms?

If anyone plans on online dating not only will you have to dodge ai robots but the real women now use a/i makeup. 

Is it a sin to wear makeup?  For males...absolutely!
There's a big difference between concealer and makeup.

Concealer is make-up ( I wear it so don't trash me)
I think what people are talking about here is more glamour make-up that doesn't just improve the natural but replaces it.

So I guess the moral of the story is that women shouldn't bathe- lol

On the contrary, she looks better without makeup.