Lather, rinse, repeat.

Constant humiliation for lies is an effective behavioral modification method.

Use it.

Kids for some reason fail to recognize that the lie-detector skills of adults are honed through our own experiences fibbing/lying as kids.  When it is an older kid, it is that much more infuriating and needs to be shut down firmly, consistently, and as humiliatingly as necessary to get the desired result.

My SS21 is a chronic liar. We don't believe anything he says without some sort of objective proof.  He lies mostly to make himself look good, he's been doing it for years. It's very similar to how BM lies to make herself look good.

When we talk about SS, we end every sentence with "Or is he?"  "SS21 says he's passing all of his classes (or is he?)"  "SS says he has a new job (or does he?)".  We truly often don't know what's true and what isn't.

You can't fix it. I can't imagine how my SS is ever going to have a healthy friendship or romantic relationship.

It sounds like it would just be a waste if time calling her out since everyone else in her life reinforces it. You will just be the wicked stepmom in her eyes. I don't think it would accomplish anything.

Started with Toxic Troll BM. She will lie till the cows come home. She cannot tell the truth to save her own life. She will either rewrite history with tiny grains of truth or just pull something out of her a$$.

SD 22 Feral Forger lies to get what she wants: money, rides, clothes, alcohol, pot, whatever, a place to stay. Used to be she lied about small weird things, now its just to be a user and abuser.

SD14almost14 Backstabber/Munchkin - shes on her way. She recently lied about school, and things I said. She had goals: get me off her back with school, and to protect phone priviledges. Now I cannot be in the same room with her for long. It doesnt get better, you get better at dealing.

What do you do about liars?

You expose them.

If they say something you know is not true, you say "YOU know that is not true"..in front of everyone.

I had a niece, close in age to me. OMG she would inflate inflate inflate stories. It drove me nuts well into my adult hood. I really liked her and she was a ton of fun to be with UNTIL.....

Example, she worked at this place WHERE some employees were engineers. Super smart simulator designers people. WELL, all of a sudden SHE worked for the DOD.

My dh is Military and DOD---I know she was NOT. She 100percent did not. But her social media bio reports she did.....BARF

Prior to that she took a semester for something random,,nothing of importance then she quit. THEN she had the guts to come back and tell everyone she was in Medical School....WTH..I finally said, STOP IT you know that is true Cathy. ----That lie went on for years. I am sure she still tells everyone she 'went to Medical School"....

I finally cut her off, completely about 5 years ago..........PEACE at last. That was after her mom, my sister died.

THEN maybe 2 years ago or so, she posted on Social Media that her Grandfather, My Dad was a famous place during a major WWII event.. It is a huge historical moment that took place. Only truth to that was my Dad was active duty during WWII, but not there.  All of these people were sending her messages OH, wow, Your Grandfather this, WOW your Grandfather was thereeeeeee, wow you must feel so proud.

.....WELL, my Dad was not there like she posted to everyone. Boy I was reallly mad. I called my brother (RIP) and he messaged her to remove her lies about HIS Father. Within minutes that LIE was removed by her.

Ooopppssss. Boy did she look like a jerk.

EXPOSE THE LIE that is what you do.

Either way, they will continue.  If you confront it, they dig deeper.  For some people it's simply pathological.  I had a cousin like this, my SD, and quite a few others.   It doesn't seem to change...at best it reduces to exaggerating.

I get it; we're dealing with this now with my SS and SD, fraternal twins age 3 1/2. We give them consequences every single time. It's helping. What is really sad is my hubby asked his daughter why she lies and she said my mommy tells lies. This little girl is watching her trash bag of a mother lie daily to everyone she knows. This is part of the reason why my husband broke up with trash bag, bc she was a habitual liar. She'd drink daily and tell him the truth drunk then forget she told him the truth and pack on more lies after she was sober. My husband won't have children with me because he had twins with trash bag 3 1/2 years ago. We really don't need anymore children but I wanted to have a child with my husband. If I was dealing with a lying adult I'd treat her like a liar. Be honest with her and tell her we can't trust you until you develop some character and morals and until then you have no privileges under this roof. Thank God Hubby and I are on the same page with discipline and how to raise the children. That would not be tolerated under our roof. 

Is SD seeing a therapist?  It sounds like the lying stems from mental illness. Usually people lie for a reason and if she is doing it just to be doing it that's not normal, especially at the rate you say.

My skids don't lie all that often, but when they do it is called out every time we see it, and there will be a consequence.  If they lie to get themselves out of trouble, we point out to them (and make sure) that the punishment for the lie exceeds what they would have gotten for the original offense.  We've also told them that if they lie, especially about stupid little stuff, they're less likely to be believed, even about important things.  If one of them has told a few lies in a short period of time, we'll ask "Why should we believe you?" even about things that are obviously true.  I don't know that this approach would work with someone who is an established, chronic liar, though.

YSD lies, fabricates, and weaves fantasies - it's part of her BPD charm and why, after her living with us as a teen, DH and I have a zero tolerance policy on lying. We confronted her each time she lied, but it's a stressful, exhausting thing having to live with someone you can't trust. I was mortified to have teachers and friends' parents come to me about it - and her therapists were aware of the problem.

I tried reasoning, punishing, explaining how hurtful lying was to others and that ultimately people would avoid her because of it - all to no avail. Even as a teen, YSD was smooth and sincere when she lied. It was just that she'd lie about things she didn't know enough about and trip herself up. For example, she bragged about travelling out of the country, but she had no passport. When she started community college, she dropped all her classes second semester but kept leaving the house each day so we wouldn't know, driving around in my convertible without insurance because she'd lied about that, too. She lost friends, family, jobs and boys due to lying, but didn't stop.

Eventually YSD took off, burning bridges everwhere she went. She told people her dad had died of brain cancer, that she had breast cancer, and then an autoimmune desease. She got pregnant, and lied about getting prenatal care. When one of her half sisters took her in, the sis even let YSD drive her car to "work" each day - until she found out YSD had lost that job but was still leaving the house each morning.  She's just a toxic hot mess, and even within my DH's dysfunctional family people keep her at arm's length because they know she's "not right".

I think all you can do is matter of factly correct your SD each time she lies. She'll learn you won't put up with it, and likely start avoiding you, which if you're lucky will lead to her moving out. Be a constant, and don't cater to her crazy. You need to be prepared for lying to be a forever part of her personality, and to detach from the drama that accompanies it. I've realized that YSD can't really have a relationship with us, because she's told so many lies over the years that it's essential she keep her relationships compartmentalized. Can't have friends, lovers, and family comparing notes, right?

Jules,

They may be toxic but unfortunately that does not mean they are totally stupid.

"Can't have friends, lovers, and family comparing notes, right?"

Even the SpermClan in our blended family world had the rare point of intelligence.  SpermGrandHag cleaned the home of the Judge that presided over our first Custody/Visitation/Support hearing.  We learned of this after the fact or we would have demanded that his honor recuse himself. 

Not that it mattered much, they lost their asses in court as it was.

I suspect that he told her to drop the custody element of the hearing because there was no way he would give her idiot son custody of my SS. At least I hope that is what happened.

His honor did spout that "Any child would be fortunate to have the love and support of this fine family." after 8 hours of the SpermIdiot arrest record, repeated career as a statutory rapist, gang affiliations, etc... dog and pony show and several people recounting SpermGrandPa's parade of mistresses.

My SS believed his lies so much that when confronted with the truth, he would be flabbergasted... it also felt like we were the only ones trying to teach him not to lie. I truly believe that when he was little, he was forced to lie about what happened at our house so he wouldn't get in trouble & his BM would feel better. Now as an adult SS can barely function in healthy relationships with others.