Renee Salt had just turned 15 when she arrived at the gates of hell. Her journey with her parents to Auschwitz, the Nazi death camp near Kraków in German-occupied Poland, was by cattle truck, wedged in with hundreds of other Jews, no food, water or air for 24 hours. On arrival, the men were separated from women and children; Renee, who was born in Poland, never saw her father again.

She and her mother stood in line. The “Angel of Death” – Nazi SS officer Josef Mengele, a doctor who conducted cruel experiments on prisoners – stood at the head of the queue. “Whenever he saw two people holding hands he would split them up with a flick of his hand, one to die and one to live,” she told the Observer. Those sent to the right were taken straight to the gas chambers. By a miracle – “God’s will, I suppose” – Renee and her mother both went to the left.

“I remember everything. In my mind, I can see everything that happened,” she said. “We were taken to a hall, everyone was stripped and had their heads shaved. They took all our possessions, jewellery, watches, everything. We were all saying prayers, hugging and kissing one another as we thought this was our last hour.”

Instead they were given a piece of white linen with a number printed on it, which they had to pin to the clothing they had been allocated – in Renee’s case, an oversized skirt and a man’s pyjama jacket. No shoes or underwear were provided. For several weeks, the prisoners sat in rows on the stone floor of a hut, day and night.

“We were taken to the latrines once a day. Also once a day they brought soup in a pan, one for every five people. There were always arguments – ‘you’ve had three sips already’. Everyone wanted the soup from the bottom of the pot because it was a bit thicker. We were not allowed to talk. We had to sleep as we were sitting.

“Twice a day we had roll calls outside the hut. Very often people collapsed from weakness. Sometimes someone would die. We were treated just like animals.”

Now aged 90, Renee will soon again stand at the gates of Auschwitz-Birkenau. Along with up to 200 other Holocaust survivors and scores of heads of state, political leaders and dignitaries, she will mark the 75th anniversary on 27 January of the camp’s liberation by Soviet soldiers. A ceremony will include speeches by survivors, and by Andrzej Duda, the Polish president, and Ronald Lauder, president of the World Jewish Congress. Britain will be represented by Camilla, Duchess of Cornwall.

Among other events to mark the anniversary and Holocaust Memorial Day is a global forum on Remembering the Holocaust: Fighting Antisemitism, at Yad Vashem, Israel’s memorial in Jerusalem, on 23 January. It will be attended by dozens of world leaders, including Emmanuel Macron, the French president, Vladimir Putin, the Russian president, Mike Pence, the US vice-president, and Frank-Walter Steinmeier, the German president. The Polish president pulled out last week, claiming he had been denied the opportunity to make a speech.

At least 1.1 million people – mostly Jews – were murdered at Auschwitz, the largest of the Nazi death camps. In the weeks before Red Army troops arrived on 27 January 1945, thousands of prisoners were shot, tens of thousands more forced on to death marches, and most of the gas chambers destroyed. About 7,000 prisoners remained.

Facebook Twitter Pinterest Renee Salt was 15 when she was sent to Auschwitz. Photograph: Antonio Olmos/the Observer

Renee Salt and her mother had been moved about four months earlier. They were first sent to do back-breaking demolition work in Hamburg, and then to the Bergen-Belsen death camp, which was liberated by British troops on 15 April 1945. Renee’s 42-year-old mother died 12 days later and was buried in a mass grave; Renee was hospitalised for several weeks.

From a huge extended family – including aunts, uncles and cousins, two sets of grandparents and even a great-grandparent – only Renee and three aunts survived the Holocaust. In 1949, she married a British soldier who had been part of the Bergen-Belsen liberation force, and the couple had two children and five grandchildren.

For decades, she never spoke of her experiences even to her immediate family, enduring frequent nightmares in isolation. But eventually she accepted an invitation to tell her story to schoolchildren, and in 2005 the BBC broadcast a documentary, Grandchild of the Holocaust, about Renee and her grandson, Adrian, then aged 13.

She returned to Auschwitz for the first time while making the programme. “I didn’t really want to go. I was shaking, I was so frightened, it was terrible. But I sort of buried the ghost,” she said.

Since then, she has returned dozens of times – but this visit may be one of the last. Seventy-five years after the end of the second world war, inevitably the number of Holocaust survivors is rapidly dwindling. At a time when antisemitism is rising once again in Europe, “this may be the last significant anniversary we commemorate with eyewitnesses who endured the unimaginable horror of the Holocaust,” said Karen Pollock of the Holocaust Educational Trust.

As well as all the facts, dates and numbers relating to the Holocaust, the world has, for many decades now, been able to “see the faces of people who did not learn about Auschwitz from books and films but actually, tangibly and physically, experienced this hell”, said Piotr Cywiński, director of the Auschwitz-Birkenau memorial and museum.

Survivors have become “moral symbols – not just of survival but also of resilience”, said Michael Berenbaum, a Holocaust scholar at the American Jewish University in California. “They bore witness to the worst humanity can be, and became voices for dignity, tolerance and decency. The idea that we’re going to lose that generation is enormously painful; we will lose the authenticity that comes from someone who can say ‘I was there’.”

But, he added, “no generation has left behind as great a historical record”, including memoirs, art, music and video testimony. “And we have been planning for a decade or so how to teach about the Holocaust in the absence of living witnesses.”

Yad Vashem holds an extensive archive of video, oral and written testimonies. In 2016, the UK National Holocaust Centre and Museum in Newark launched an innovative way of preserving the responses of survivors to children’s questions. The Forever Project has created lifesize images of survivors which, using digital technology, can “answer” questions in real time from hundreds of pre-recorded replies. The centre has also produced a short film, telling the story of one survivor through the medium of hip-hop, as a means of engaging young people.

“In a climate of ignorance, trivialisation and denial, the primacy of first-hand testimony cannot be overstated,” said Marc Cave, the centre’s chief executive. “The Forever Project is the single most important thing we’ve done to future-proof Holocaust education for generations to come.”

Facebook Twitter Pinterest Children found at Auschwitz after the liberation of the camp in 1945. Photograph: AP

There is also “secondary testimony” – accounts from children and grandchildren of their parents’ and grandparents’ stories. But many survivors’ descendents also have their own stories to tell of living in the long shadow of the Holocaust.

The impact on the “second generation” has been extensively researched, with psychologists and academics noting symptoms of trauma such as clinical depression, anxiety, addiction and eating disorders among some descendants. Now it is being acknowledged that some of the third generation are also struggling under the weight of family history.

Allison Nazarian’s maternal grandparents survived Auschwitz and Bergen-Belsen, where her mother was born. She has written a book, Aftermath: A Granddaughter’s Story of Legacy, Healing and Hope, about her third-generation experience. “I was close to my grandparents. They freely and graphically talked of their lives during the Holocaust. I absorbed their experiences. It was all I heard about. I was surrounded by the Holocaust; it was part of every story, every discussion, every day of my life,” she said.

“I was told, ‘they could come for us at any time, you have to be ready’. Even now, I have a ‘go bag’ with passports and essentials. There are certain things I have an irrational fear of running out of. It was only at 12 or 13 I realised not everyone’s grandparents were in the Holocaust. It made me who I am.”

Now 48, Nazarian decided she would not expose her children – the fourth generation – to the same trauma. “I don’t want it to sound as if I’m resentful or regretful – I’m very proud of my grandparents. But I don’t think passing on the burden would help. My children are 100% free of it.”

A second-generation survivor, Naomi Levy, said descendants had a strong sense of an “overall sense of loss and ghosts from the pasts”. She went through a period of “trying to repel, to push it away” but eventually embraced researching and recording her family history, “trying to piece everything together”.

With regard to her own children, now adults, she said: “I wanted to protect them from it for as long as possible. I was very careful around the subject as they grew up. It’s a balancing act – I don’t want it to be a burden, but it is what it is. I think they will want to know more, but I’m not going to make them face it.”

In Israel, a small number of third-generation survivors have had their grandparents’ camp identification numbers tattooed on their own arms as a memorial. The trend, although limited, has been controversial and shocking to many, and not just because of the Jewish prohibition on tattoos.

But, for many, the young people’s motive – “never forget” – is more relevant than ever in a time of rising antisemitism, nationalism and populism. According to Cywiński, the significance of this year’s anniversary lies not just in the number of years since the liberation of Auschwitz, but is “related to the world we live in today. Antisemitism, racist and xenophobic reactions are being revived on an unexpected scale, and groups that openly promote hatred are on the rise. All this in the profound helplessness of our democratic institutions, weakened by populism and demagoguery, which have been reborn in so many countries around the world”.

It was a mistake to put the Holocaust into a box marked “history”, said Cave. “When we see lesbians beaten up on a bus or monkey chants at a football match, these are symptoms of ‘othering’ – and that’s exactly how the Holocaust and most genocides start. There is no greater lesson than the warning from history of the Holocaust.”

Renee Salt has told her story over and over again “so that people shouldn’t forget. There are still people who say it didn’t happen, there are still deniers. But you can’t hide people like me away. At the end of the war, we believed what happened could never and would never happen again. But now it’s a worrying time.”

In memory

Auschwitz-Birkenau

An official memorial event will mark the 75th anniversary of the liberation of the Nazi death camp on 27 January, International Holocaust Remembrance Day. Up to 200 Holocaust survivors who were imprisoned at the camp will attend, along with heads of state from at least 22 countries. A ceremony at 3.30pm will be addressed by survivors, Poland’s president Andrzej Duda, and Ronald Lauder, president of the World Jewish Congress. It will end with the kaddish, the Jewish prayer for the dead.

Yad Vashem

A forum under the banner Remembering the Holocaust, Fighting Antisemitism will be held at Yad Vashem, the Holocaust memorial near Jerusalem. More than 40 state leaders, royals and other dignitaries will be there. Prince Charles will represent the UK as part of his first official visit to Israel. As well as meeting Holocaust survivors, Charles will also visit Bethlehem and meet Palestinian president Mahmoud Abbas. (A tweet last month from the British consulate in East Jerusalem welcoming Charles’s visit to the “Occupied Palestinian Territories” was met with an undiplomatic riposte from Yair Netanyahu, the son of Israeli PM Benjamin Netanyahu. “God willing you guys will be kicked out of Israel soon. Until then I’m thinking of visiting the occupied lands of Scotland or Wales, which do you recommend?” the younger Netanyahu tweeted.)

The BBC

In the run-up to the anniversary, the BBC is broadcasting a range of documentaries and dramas, plus Songs of Praise from the UK National Holocaust Centre and Museum and live coverage of the commemoration in Poland. “We’re offering everyone the chance to reflect on the consequences of prejudice and hatred, and in doing so we’ll ensure that the millions of lives lost in the Holocaust are not forgotten,” said Tony Hall, the BBC’s director general.

The UK National Holocaust Centre and Museum

The centre in Nottinghamshire – founded by a Christian family in 1991 – is taking a virtual reality exhibition, The Eye As Witness, around the country. It invites people to think critically about propaganda techniques and racism and hatred today.

75 Memorial Flames exhibition

The Holocaust Memorial Day Trust invited organisations and community groups, including prisons, schools and faith groups, to make artworks featuring a memorial flame. Seventy-five have been chosen for an exhibition that will launch at the memorial day ceremony in Westminster on 27 January and then tour the UK.

• This article was amended on 13 January 2020 to refer, in accordance with the Guardian style guide, to Auschwitz-Birkenau having operated in Poland during the period Poland was occupied by Nazi Germany. It was further amended on 15 January 2020 to more correctly refer to the troops who liberated the camp as Soviet, not “Russian”.