TL;DR: No book fixes one correct number of incense sticks for every altar. The common folk custom is to burn an odd number, usually 1 stick on ordinary days and 3 on the full moon, the first day of the lunar month and death anniversaries, because odd numbers are considered yang; the root of that division is the line "heaven one, earth two" in the Great Commentary of the I Ching, where odd numbers are the numbers of Heaven. Việt Nam phong tục by Phan Kế Bính describes burning incense on many occasions but records only "one stick", "a few sticks" and "three or five sticks", without laying down a rule of odd numbers.
How many incense sticks should you burn?
There is no single correct number for every altar. The common Vietnamese custom is to burn an odd number: usually 1 stick on ordinary days, 3 sticks on the full moon, the first day of the lunar month and death anniversaries; at large ceremonies in communal houses and temples, some places burn 5 or 7. Even numbers, especially 2 sticks, are usually avoided.
Old books do not set down that rule. Việt Nam phong tục by Phan Kế Bính describes burning incense on many occasions, from ancestral offerings to funerals, but records only "one stick", "a few sticks" or "three or five sticks", never saying it must be an odd number[2][3].
What does Việt Nam phong tục say about burning incense?
Phan Kế Bính traces the origin of the incense-burning custom to an old Chinese story: in the reign of Emperor Wu of Han, sacrifices at the ancestral temple burned only fragrant grass mixed with fat, until the Hunjia state in the Western Regions presented a golden statue of a deity, whose people worshipped it with incense and prostration alone, and from that time the custom of burning incense arose; he explains burning incense as "praying for ghosts and spirits to descend"[1]. As for our country, he writes that "the custom of burning incense is of unknown origin", citing the Records of Wu, which tells of Zhang Jin, governor of Jiaozhou, who often burned incense while reading Daoist texts[1].
The occasions involving incense recorded in books and research, together with the number of sticks noted:
| Occasion | What is recorded | Source |
|---|---|---|
| Lowering the coffin into the grave at rural funerals | After the earth is filled in, each person holds one incense stick, chants sutras and walks around the grave | Việt Nam phong tục[2] |
| Quyên giáo at the temple gate | Burning three or five incense sticks placed in a vase beside the tray collecting donations | Việt Nam phong tục[3] |
| The Bà festival of the Chinese community in Huế (former Thừa Thiên Huế province) | Three long red Chinese-style incense sticks are lit in each incense bowl | Dương Thị Hải Vân, 2018[5] |
| Shrines to goddesses in Huế | An incense stick is burned on the full moon, the first day of the lunar month and the village festival day | Dương Thị Hải Vân, 2023[6] |
Of those four rows, only the row for the Chinese community in Huế has a fixed number; the other rows show that the number of sticks follows the occasion and the person, not a rule.
Why is an odd number usually burned?
The root of treating odd numbers as yang numbers lies in the Great Commentary, part one, of the I Ching: "Heaven one, earth two, heaven three, earth four, heaven five, earth six, heaven seven, earth eight, heaven nine, earth ten", meaning 1, 3, 5, 7, 9 are the numbers of Heaven and 2, 4, 6, 8, 10 are the numbers of Earth[4]. This passage is about the numbers used in the yarrow-stalk method of casting hexagrams, not about incense.
Folk practice links that division to offerings: Heaven is yang, the affairs of the living are yang, so incense offered upward uses odd numbers; even numbers are yin and so are avoided. People also assign separate meanings to each number: 3 sticks are usually explained as the Three Jewels (Buddha, Dharma, Sangha) at a Buddha altar, or Heaven, Earth and Humanity at an ancestral altar; 5 sticks are the Five Elements. These are local explanations, and no book serves as the standard.
Is it acceptable to burn just 1 incense stick?
Yes, and this is how many families burn incense daily; one stick is understood as sincerity, and the number of sticks is not a measure of sincerity.
At the goddess shrines that Dương Thị Hải Vân surveyed in Huế (former Thừa Thiên Huế province), the worship is described as simple, with an incense stick burned only on the full moon, the first day of the lunar month and the village festival day[6]. Việt Nam phong tục, describing the rite of announcing to the ancestors at each weekly and seasonal observance and on death anniversaries, records only "lighting the lamp and burning incense, praying to the ancestors according to the occasion", without specifying a number of sticks[8].
Why is burning 2 incense sticks avoided?
Two is an even number and, by the division above, belongs to yin, so folk belief holds that burning 2 sticks on an altar is not proper for the rite. This is an orally transmitted taboo; books of customs record no prohibition, and some families still burn even numbers according to their own clan tradition.
Does incense smoke affect health?
Yes. A 2008 medical review by Lin, Krishnaswamy and Chi, compiling studies, shows that incense smoke produces particulate dust, gases and organic compounds, and is associated with respiratory diseases. So in a closed altar room, burning fewer sticks and opening a door for ventilation is a way to reduce smoke without giving up the rite.
Nhật Nguyệt's suggestion: a household without its own custom can keep to the common practice, 1 stick on ordinary days and 3 sticks on the full moon, the first day of the lunar month and death anniversaries; when visiting a communal house, temple or pagoda, follow that place's way of burning, since each place has its own rule.
