Baby bottle

A baby bottle is a bottle with a teat (also called a nipple in the US) to drink directly from. It is typically used if someone can not (as conveniently) drink from a cup, for feeding oneself or being fed.

In particular it is used to feed an infant with infant formula, expressed breast milk or pediatric electrolyte solution.

Dimensions and design
A large-sized bottle typically holds 270 ml; the small size 150 ml. It is composed of a bottle itself, a teat, a ring to seal the teat to the bottle, a cap to cover the teat and optionally a disposable liner.

The height-to-width ratio of bottles is high (relative to adult cups) because it is needed to ensure the contents flood the teat when used at normal angles; otherwise the baby will drink air. However, if the bottle is too tall, it easily tips. There are asymmetric bottles that ensure the contents flood the teat if the bottle is held at a certain direction.

Teats (or nipples)
The teat itself is typically slimmer and more flexible than the mother's nipple. Babies can find feeding from the bottle easier than breastfeeding. Specialized teats that mimic the shape of the breast exist to allow babies to switch back and forth between bottle feeding and breast feeding for cases where "teat confusion" occurs. Teats come in a selection of flow rates. Different flow rate teats either have more holes or larger holes. The correct flow rate needs to selected based on the age of the infant. Variable flow rate teats are available for older infants. The hole is asymmetric so that by turning the bottle/teat, different flows can occur. Specialized teats are available for infants with cleft palate (see also Haberman feed).

Vented bottles
"Vented" bottles allow air to enter the bottle while the baby is drinking without the need to break the baby's suction during feeding. Alternatively a bottle liner can be used to enclose the formula instead of directly in the bottle. The liner collapses as the formula is drained.

Vented bottles work by allowing air to enter while preventing the liquid inside from escaping. Avent is the most popular brand in this category. It works by an "anti-vacuum skirt" in the base of the teat, where it forms a seal with the bottle. The skirt acts as a one way valve, allowing air to enter the bottle but not liquids to leave. If the sealing ring is tightened too much, the skirt is compressed too tightly to allow it to open and the bottle will not vent. If the sealing ring is too loose, liquid leaks from the bottle.

There are multiple patents for technologies in this area. Initial designs called for a complex spring and valve system that was impossible to clean and sterilize. Current research is in specialized materials with microscopic pores that allow the entry of air without the escape of liquids. This avoids the caregiver having to get the sealing ring tension just right. It remains to be seen whether these materials can withstand the rigours of daily cleaning and sterilization. Another competitor, Dr. Brown's, offers a system whereby the vented air is conducted through a tube to the bottom of the bottle where the airspace is when the bottle is in use. This avoids the vented air from bubbling through the liquid and unnecessarily aerating the liquid.

Variations and accessories
Bottles may be designed to attach directly to a breast pump for a complete "feeding system" that maximizes the reuse of the components. Such systems include a variety of drinking spouts for when the child is older. This converts the bottle into a sippy cup, a cup with lid and spout for toddlers, which is intermediate between a baby bottle and an open top cup. Bottles that are part of a feeding system may include handles that can be attached. The ring and teat may be replaced by a storage lid.

Accessories for bottles include cleaning brushes and drying racks. Brushes may be specially designed for a specific manufacturer's bottles and teats. Bottle warmers warm previously made and refrigerated formula. Cooler designed to fit a specific manufacturer's bottles are available to keep refrigerated formula cold. Special formula powder containers are available to store pre-measured amounts of formula so that caregivers can pre-fill bottles with sterile water and mix in the powder easily. The containers are typically designed to stack together so that multiple pre-measured amounts of formula powder may be transported as a unit.

Specialty, "designer" bottles are now quite common as novelty gifts for parents or just something interesting for the child. They either have special logos or are of special shapes (e.g. animals). Some even have a hole in the middle. Depending on the shape, these bottles can be quite difficult to clean. Another specialty bottle is made from heat sensitive materials that act as a built-in thermometer. If the contents are too hot, the bottle changes color.

Institutions can purchase ready-to-feed formula in containers that can be used as baby bottles. The lid screws off and is replaced by a disposable teat when the formula is ready to be used. This avoids storing the formula with the teat and possibly clogging the teat holes when formula is splashed within the bottle and dries.

Sterilization
If necessary, bottles can be sterilized by boiling in hot water, in a specialized bottle sterilization appliance (which typically uses steam) or in a specialized sterilization container that is microwaved. Modern bottles are difficult to sterilize in boiling water because they tend to float. Bottles were originally composed of glass which was dangerous when babies learned to feed themselves and held the bottle. For mainly cost reasons, modern bottles are unbreakable plastic. Since bottles have to be made to withstand the heat of sterilization, the bottle can also withstand the heat of dishwashers and are dishwasher-safe.

There is some concern about BPA leakage on polycarbonate bottles due to extended dishwasher or boiling. However, unless there are infant health concerns, or concerns about water contamination, baby bottle sterilization can be replaced by cleaning with hot soapy water.

Regulation
While infant formula is highly regulated, baby bottles are not. Only the materials of the teat and bottle itself are specifically regulated in some countries (e.g. British Standards BS 7368:1990 "Specification for babies' elastomeric feeding bottle teats" ). In the USA, the Food and Drug Administration (FDA) also regulates teats and the bottle materials. In 1985 it tightened allowable levels of nitrosamines released from bottle teats. A 1999 Consumer Reports study suggesting that plastic bottles release unsafe amounts of bisphenol A was denounced as sensationalism because of the unreasonable conditions the bottles were subject to. Findings since, however, have renewed the initial concerns (see Bisphenol A - Possible Health Risks).  More research is needed.

History
Bottles with hard spouts go back to prehistory. "The first consisted of urns with two openings: one for pouring the liquid into the bottle and the other to be put in the baby's mouth." Soft teats of various materials were tried but were very difficult to clean. The invention of vulcanized rubber provided a material that was soft and could withstand the heat of sterilization. Elijah Pratt of New York patented the first rubber teat in 1845. It took until the 1900s before the technology was perfected for a practical soft teat such that the baby bottle could become a practical and safe alternative to breastfeeding.

In the UK in 1999, "the feeding and sterilising equipment sector ... stands at £49m. Sales of feeding bottles account for 39% of the market" , or £19.1m.