diff --git a/CHANGELOG.md b/CHANGELOG.md
index 689c7d338..49943e927 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -112,6 +112,7 @@ and this project adheres to
 * [household] bugfix if position of member is null, renderbox no longer throws an error (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/480)
 * [parcours] location cannot be removed if linked to a user (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/478)
 * [person] email added to twig personRenderbox (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/490)
+* [activity] Only youngest descendant is kept for social issues and actions (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/471)
 * [person] Add link to current household in person banner (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/484)
 * [address] person badge in address history changed to open OnTheFly with all person info (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/489)
 * [person] Change 'personne' with 'usager' and '&' with 'ET' (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/499)
@@ -139,6 +140,9 @@ and this project adheres to
 * [notification] Display of social action within workflow notification set to display block (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/537)
 * [onthefly] trim trailing whitespace in email of person and thirdparty (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/542)
 
+* [action] Only youngest descendant is kept for social issues and actions (https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/471)
+## Test releases
+
 ### test release 2022-02-21
 
 * [notifications] Word 'un' changed to number '1' for notifications in user menu (https://gitlab.com/champs-libres/departement-de-la-vendee/accent-suivi-developpement/-/issues/483)
diff --git a/src/Bundle/ChillActivityBundle/Entity/Activity.php b/src/Bundle/ChillActivityBundle/Entity/Activity.php
index 0a344236c..eabaa44d1 100644
--- a/src/Bundle/ChillActivityBundle/Entity/Activity.php
+++ b/src/Bundle/ChillActivityBundle/Entity/Activity.php
@@ -231,11 +231,22 @@ class Activity implements AccompanyingPeriodLinkedWithSocialIssuesEntityInterfac
     {
         if (!$this->socialActions->contains($socialAction)) {
             $this->socialActions[] = $socialAction;
+            $this->ensureSocialActionConsistency();
         }
 
         return $this;
     }
 
+    /**
+     * Add a social issue.
+     *
+     * Note: the social issue consistency (the fact that only yougest social issues
+     * are kept) is processed by an entity listener:
+     *
+     * @see{\Chill\PersonBundle\AccompanyingPeriod\SocialIssueConsistency\AccompanyingPeriodSocialIssueConsistencyEntityListener}
+     *
+     * @return $this
+     */
     public function addSocialIssue(SocialIssue $socialIssue): self
     {
         if (!$this->socialIssues->contains($socialIssue)) {
@@ -631,4 +642,13 @@ class Activity implements AccompanyingPeriodLinkedWithSocialIssuesEntityInterfac
 
         return $this;
     }
+
+    private function ensureSocialActionConsistency(): void
+    {
+        $ancestors = SocialAction::findAncestorSocialActions($this->getSocialActions());
+
+        foreach ($ancestors as $ancestor) {
+            $this->removeSocialAction($ancestor);
+        }
+    }
 }
diff --git a/src/Bundle/ChillActivityBundle/Tests/Entity/ActivityTest.php b/src/Bundle/ChillActivityBundle/Tests/Entity/ActivityTest.php
new file mode 100644
index 000000000..7a68a36fc
--- /dev/null
+++ b/src/Bundle/ChillActivityBundle/Tests/Entity/ActivityTest.php
@@ -0,0 +1,114 @@
+<?php
+
+/**
+ * Chill is a software for social workers
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Chill\ActivityBundle\Tests\Entity;
+
+use Chill\ActivityBundle\Entity\Activity;
+use Chill\PersonBundle\AccompanyingPeriod\SocialIssueConsistency\AccompanyingPeriodSocialIssueConsistencyEntityListener;
+use Chill\PersonBundle\Entity\AccompanyingPeriod;
+use Chill\PersonBundle\Entity\SocialWork\SocialAction;
+use Chill\PersonBundle\Entity\SocialWork\SocialIssue;
+use Doctrine\ORM\Event\LifecycleEventArgs;
+use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
+
+/**
+ * @internal
+ * @coversNothing
+ */
+final class ActivityTest extends TestCase
+{
+    use ProphecyTrait;
+
+    public function testHierarchySocialActions(): void
+    {
+        $parent = new SocialAction();
+        $child = new SocialAction();
+
+        $parent->addChild($child);
+        $grandChild = new SocialAction();
+        $child->addChild($grandChild);
+
+        $activity = new Activity();
+
+        $activity->addSocialAction($parent);
+
+        $this->assertCount(1, $activity->getSocialActions());
+        $this->assertContains($parent, $activity->getSocialActions());
+
+        $activity->addSocialAction($grandChild);
+
+        $this->assertCount(1, $activity->getSocialActions());
+        $this->assertContains($grandChild, $activity->getSocialActions());
+        $this->assertNotContains($parent, $activity->getSocialActions());
+
+        $activity->addSocialAction($child);
+
+        $this->assertCount(1, $activity->getSocialActions());
+        $this->assertContains($grandChild, $activity->getSocialActions());
+        $this->assertNotContains($parent, $activity->getSocialActions());
+        $this->assertNotContains($child, $activity->getSocialActions());
+
+        $activity->addSocialAction($another = new SocialAction());
+
+        $this->assertCount(2, $activity->getSocialActions());
+        $this->assertContains($grandChild, $activity->getSocialActions());
+        $this->assertContains($another, $activity->getSocialActions());
+        $this->assertNotContains($parent, $activity->getSocialActions());
+        $this->assertNotContains($child, $activity->getSocialActions());
+    }
+
+    public function testHierarchySocialIssues(): void
+    {
+        $listener = new AccompanyingPeriodSocialIssueConsistencyEntityListener();
+        $event = $this->prophesize(LifecycleEventArgs::class)->reveal();
+
+        $parent = new SocialIssue();
+        $child = new SocialIssue();
+
+        $parent->addChild($child);
+        $grandChild = new SocialIssue();
+        $child->addChild($grandChild);
+
+        $activity = new Activity();
+        $activity->setAccompanyingPeriod(new AccompanyingPeriod());
+
+        $activity->addSocialIssue($parent);
+        $listener->preUpdate($activity, $event);
+
+        $this->assertCount(1, $activity->getSocialIssues());
+        $this->assertContains($parent, $activity->getSocialIssues());
+
+        $activity->addSocialIssue($grandChild);
+        $listener->preUpdate($activity, $event);
+
+        $this->assertCount(1, $activity->getSocialIssues());
+        $this->assertContains($grandChild, $activity->getSocialIssues());
+        $this->assertNotContains($parent, $activity->getSocialIssues());
+
+        $activity->addSocialIssue($child);
+        $listener->preUpdate($activity, $event);
+
+        $this->assertCount(1, $activity->getSocialIssues());
+        $this->assertContains($grandChild, $activity->getSocialIssues());
+        $this->assertNotContains($parent, $activity->getSocialIssues());
+        $this->assertNotContains($child, $activity->getSocialIssues());
+
+        $activity->addSocialIssue($another = new SocialIssue());
+        $listener->preUpdate($activity, $event);
+
+        $this->assertCount(2, $activity->getSocialIssues());
+        $this->assertContains($grandChild, $activity->getSocialIssues());
+        $this->assertContains($another, $activity->getSocialIssues());
+        $this->assertNotContains($parent, $activity->getSocialIssues());
+        $this->assertNotContains($child, $activity->getSocialIssues());
+    }
+}
diff --git a/src/Bundle/ChillPersonBundle/Entity/SocialWork/SocialAction.php b/src/Bundle/ChillPersonBundle/Entity/SocialWork/SocialAction.php
index ec5e5a8e5..904950489 100644
--- a/src/Bundle/ChillPersonBundle/Entity/SocialWork/SocialAction.php
+++ b/src/Bundle/ChillPersonBundle/Entity/SocialWork/SocialAction.php
@@ -128,6 +128,44 @@ class SocialAction
         return $this;
     }
 
+    /**
+     * In a SocialIssues's collection, find the elements which are an ancestor of
+     * other elements.
+     *
+     * The difference of the given list (thus, the elements which are **not** kept
+     * in the returned collection) are the most-grand-child elements of the list.
+     *
+     * Removing those elements of the Collection (which is not done by this method)
+     * will ensure that only the most descendent elements are present in the collection,
+     * (any ancestor of another element are present).
+     *
+     * @param Collection|SocialAction[] $socialActions
+     *
+     * @return Collection|SocialAction[] a list with the elements of the given list which are parent of other elements in the given list
+     */
+    public static function findAncestorSocialActions(Collection $socialActions): Collection
+    {
+        $ancestors = new ArrayCollection();
+
+        foreach ($socialActions as $candidateChild) {
+            if ($ancestors->contains($candidateChild)) {
+                continue;
+            }
+
+            foreach ($socialActions as $candidateParent) {
+                if ($ancestors->contains($candidateParent)) {
+                    continue;
+                }
+
+                if ($candidateChild->isDescendantOf($candidateParent)) {
+                    $ancestors->add($candidateParent);
+                }
+            }
+        }
+
+        return $ancestors;
+    }
+
     /**
      * @return Collection|self[]
      */
@@ -169,7 +207,7 @@ class SocialAction
     }
 
     /**
-     * @return Collection|self[] All the descendants with the current entity (this)
+     * @return Collection|self[] All the descendants including the current entity (this)
      */
     public function getDescendantsWithThis(): Collection
     {
@@ -233,6 +271,23 @@ class SocialAction
         return $this->getParent() instanceof self;
     }
 
+    /**
+     * Recursive method which return true if the current $action
+     * is a descendant of the $action given in parameter.
+     */
+    public function isDescendantOf(SocialAction $action): bool
+    {
+        if (!$this->hasParent()) {
+            return false;
+        }
+
+        if ($this->getParent() === $action) {
+            return true;
+        }
+
+        return $this->getParent()->isDescendantOf($action);
+    }
+
     public function removeChild(self $child): self
     {
         if ($this->children->removeElement($child)) {
diff --git a/src/Bundle/ChillPersonBundle/Entity/SocialWork/SocialIssue.php b/src/Bundle/ChillPersonBundle/Entity/SocialWork/SocialIssue.php
index c735c0132..fb277f56c 100644
--- a/src/Bundle/ChillPersonBundle/Entity/SocialWork/SocialIssue.php
+++ b/src/Bundle/ChillPersonBundle/Entity/SocialWork/SocialIssue.php
@@ -202,7 +202,7 @@ class SocialIssue
     }
 
     /**
-     * @return Collection|self[] All the descendants with the current entity (this)
+     * @return Collection|self[] All the descendants including the current entity (this)
      */
     public function getDescendantsWithThis(): Collection
     {