Thailand's safety picture for solo travellers is dominated by one activity. Everything else is minor by comparison, and getting the proportions right matters.
The scooter, which is the whole thing
Scooter and motorbike accidents are the most common cause of serious injury to visitors in Thailand, by a large margin.
You legally need the correct motorcycle category on an international driving permit, and almost all travel insurance voids cover for an accident without it.
That means a hospital bill or an air ambulance paid personally, and Thai medical costs for a serious injury run into tens of thousands.
Rental shops hire to anyone. They are not carrying the risk.
Wear a helmet. Island road surfaces are worse than they look, and gravel on bends is the standard cause.
The passport deposit
Never leave your passport as a rental deposit.
It is a common request and a common lever in disputed damage claims — the passport is held until an inflated repair bill is paid, and you have no leverage.
Offer a cash deposit or a photocopy, and photograph the vehicle thoroughly from all angles before riding away.
Water
Riptides cause drownings every year, particularly on the Andaman coast during the May to October monsoon.
Red flags are posted and are frequently ignored. They are not decorative.
The escape is to swim parallel to the shore rather than against the current, then back in at an angle.
Swim where there are others, and not after drinking.
The scams
The temple closed scam — someone near the Grand Palace or Wat Pho says the site is shut for a ceremony and offers an alternative tuk-tuk itinerary ending at a gem or tailor shop. It is not shut. Walk to the official entrance.
Jet ski damage claims — pre-existing damage attributed to you on return. Photograph everything first, or do not rent one.
Taxi meter refusal. If they quote a fixed price, take another.
Very cheap tours that include a gem or jewellery stop where the operator takes commission.
None of these are dangerous. They are financial and they are avoidable.
What is genuinely fine
Thailand is a straightforward country to travel alone. Violent crime against visitors is rare, transport is reliable, and the tourist infrastructure is mature.
Solo women travel Thailand in large numbers and report it as easy, with normal urban precautions.
The precautions worth taking
Insurance that covers what you will actually do, with the exclusions read rather than the summary — diving depth, motorcycling, and any adventure activity.
Watch your drink being poured and do not leave it, which applies everywhere.
Share your plans with someone, particularly when moving between islands.
Know where the nearest hospital is. Thai private hospitals in the main tourist areas are excellent and will want payment or insurance confirmation up front.
Carry a card with your accommodation's name in Thai, which every guesthouse will give you.
The honest summary
Do not ride a scooter without the licence. Respect red flags. Everything else is ordinary travel caution.