Short answer
Wearing them while you are not praying is not haram in itself, but you must remove them before the ghusl that ends your period. Acrylic, gel or press-on nails stop water reaching the nail, so a ghusl done with them on is not valid, and nor are the prayers that follow. All four schools agree that water must reach every part of the body.
Adornment for one's husband or among women is permitted. But anything that blocks water from the skin or nail must be removed for ghusl, because washing the whole body is fard. A ghusl with fake nails on is invalid.
The four schools agree on this.
Explanation
Some women time their nails for their period, since they are not praying anyway. The adornment itself is not the problem. The problem comes at the end of the period: ghusl requires water to reach every part of the body, including the nails. The Prophet ﷺ once saw a man whose foot had a dry spot the size of a fingernail after wudu and told him to go back and do it properly. If a nail-sized gap spoils wudu, a whole set of acrylics spoils ghusl.
What this means in practice:
- Press-on nails: easy to remove. Take them off before your ghusl.
- Acrylic or gel extensions: they must come off before ghusl, which usually means a salon visit or soaking. Plan for this before your period ends, or you will be delaying prayers.
- If you did ghusl with them on: your ghusl did not count. Remove them, repeat the ghusl, and make up the prayers you prayed in the meantime.
- Showing them in public: long decorated nails are adornment, so keep them for home and women's gatherings.
Also keep in mind that cutting the nails is part of the fitrah, and the Companions were given a limit of forty days. Nail polish follows the same rule as fake nails; see praying with nail polish and wudu with nail polish. For the steps of ghusl, see how to do ghusl.
The evidence
Quran, Surah Al-Maaida 5:6
يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓا۟ إِذَا قُمْتُمْ إِلَى ٱلصَّلَوٰةِ فَٱغْسِلُوا۟ وُجُوهَكُمْ وَأَيْدِيَكُمْ إِلَى ٱلْمَرَافِقِ وَٱمْسَحُوا۟ بِرُءُوسِكُمْ وَأَرْجُلَكُمْ إِلَى ٱلْكَعْبَيْنِ ۚ وَإِن كُنتُمْ جُنُبًۭا فَٱطَّهَّرُوا۟ ۚ وَإِن كُنتُم مَّرْضَىٰٓ أَوْ عَلَىٰ سَفَرٍ أَوْ جَآءَ أَحَدٌۭ مِّنكُم مِّنَ ٱلْغَآئِطِ أَوْ لَٰمَسْتُمُ ٱلنِّسَآءَ فَلَمْ تَجِدُوا۟ مَآءًۭ فَتَيَمَّمُوا۟ صَعِيدًۭا طَيِّبًۭا فَٱمْسَحُوا۟ بِوُجُوهِكُمْ وَأَيْدِيكُم مِّنْهُ ۚ مَا يُرِيدُ ٱللَّهُ لِيَجْعَلَ عَلَيْكُم مِّنْ حَرَجٍۢ وَلَٰكِن يُرِيدُ لِيُطَهِّرَكُمْ وَلِيُتِمَّ نِعْمَتَهُۥ عَلَيْكُمْ لَعَلَّكُمْ تَشْكُرُونَ ﴿٦﴾
O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles. And if you are in a state of janabah, then purify yourselves. But if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and do not find water, then seek clean earth and wipe over your faces and hands with it. Allah does not intend to make difficulty for you, but He intends to purify you and complete His favor upon you that you may be grateful.
Ghusl means purifying the whole body, which a barrier prevents.
Sahih Muslim 243
Sahih... ارجع فأحسن وضوءك ...
"Go back and do your wudu properly."
Said to a man who left a nail-sized dry spot, showing that a small barrier spoils purification.
Sahih al-Bukhari 60
Sahih... ويل للأعقاب من النار ...
"Woe to the heels from the Fire."
A warning against leaving any part unwashed.
Where the ruling is recorded
- Nur al-Idah with Maraqi al-Falah, Kitab al-Taharah, chapter on ghusl. Washing the whole outer body is fard, and anything that stops water reaching the skin must be removed.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Taharah, the obligations of ghusl. A barrier on the nails, such as dough or wax, prevents a valid ghusl.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.