Ceremonial or symbolic helmets (e.g. UK policeman's helmet) without protective function are at times used. The oldest known use of helmets was by Assyrian soldiers in 900 BC, who wore thick leather or bronze helmets to protect the head from blunt object and sword blows and arrow strikes in combat. Soldiers still wear helmets, now often made from lightweight plastic materials.
In civilian life, helmets are used for recreational activities and sports (e.g. jockeys in horse racing, American football, ice hockey, cricket, baseball, camogie, hurling and rock climbing); dangerous work activities (e.g. construction, mining, riot police); and transportation (e.g. Motorcycle helmets and bicycle helmets). Since the 1990s, most helmets are made from resin or plastic, which might be reinforced with fibres such as aramids.
The word helmet is diminutive from helm, a mediaeval word for protective combat headgear. The Medieval great helm covers the whole head and often is accompanied with camail protecting throat and neck as well. Originally a helmet was a helm which covered the head only partly.
All helmets attempt to protect the user's head by absorbing mechanical energy and protecting against penetration. Their structure and protective capacity are altered in high-energy impacts. Beside their energy-absorption capability, their volume and weight are additionally important issues, after higher volume and weight increase the injury risk for the user's head and neck. Anatomical helmets adapted to the inner head structure were invented by neurosurgeons at the end of the twentieth century.
Helmets used for different purposes have different designs. For example, a bicycle helmet must protect against blunt impact forces from the wearer's head striking the road. A helmet designed for rock climbing must protect against heavy impact, and against objects such as small rocks and climbing equipment falling from above. Practical concerns additionally dictate helmet design: a bicycling helmet should be aerodynamic in shape and well ventilated, while a rock climbing helmet must be lightweight and small so that it doesn't interfere with climbing.
Some helmets have additional protective elements attached to them, such as a face visors or goggles or a face cage, or an ear cage or ear plugs and additional forms of protective headgear, and a communications system. Sports helmets might have an integrated metal face protector (face cage).
- Baseball batting helmets have an expanded protection over the ear, which protects the jaw from injury.
- Motorcycle helmets often have flip-down face screens for rain and wind protection, and they might additionally have projecting visors to protect the eyes from glare.
- Hard hats for construction workers are worn mainly to protect the wearer from falling objects such as tools.
- Helmets for riot police often have flip-down clear visors and thick padding to protect the back of the neck.
- Modern firefighter's helmets protect the face and back of the head against impact, fires and electricity, and can include masks, communication systems, and additional accessories.
- Welding helmets protect the eyes and face and neck from flash burn, ultraviolet light, sparks and heat. They have a small window, called a lens shade, through which the welder looks at the weld; for arc welding this window must be much darker than in blowtorch goggles and sunglasses.
- People with a few medical conditions must wear a helmet to protect the brain, due to a gap in the braincase, e.g. because of cleidocranial dysostosis or in separated craniopagus twins.
- Mixed martial arts helmets have ear pads to prevent serious injuries to the athletes, who don't usually endure such force to the ears.
- Some watersports helmets, such as for underwater hockey or water polo, have ear-cages fitted which are designed to help prevent burst eardrums caused by an excessive water pressure resulting from a contact or percussion from additional equipment involved in the sport.
- Crash helmets for F1 racing drivers, their design and construction have evolved enormously. Nevertheless, head and neck trauma remains the greatest single injury risk to drivers.
Historically, helmets have been made from a wide range of materials, including various metals, plastics, leather, and even a few fibrous materials such as Kevlar. Ancient and mediaeval helmets were usually made of metals, often bronze, iron or steel, though a few boar's tusk helmets were known to ancient Mycenea.
Some British gamekeepers throughout the eighteenth and nineteenth centuries wore helmets made of straw bound together with cut bramble. Developed in the mid-19th century, the pith helmet, made of pith or cork, was often worn by Europeans in the tropics.
Military applications in the 19th-20th centuries saw a number of leather helmets, particularly among aviation and tanker crews in the early twentieth century. In the early days of the automobile, a few motorists additionally adopted this style of headgear, and early football helmets were additionally made of leather. In World War II, American, Soviet, German, Italian and French flight crews wore leather helmets, the German pilots disguising theirs under a beret before disposing of both and switching to cloth caps. The era of the First and Second World Wars additionally saw a resurgence of metal military helmets, most notably the Brodie helmet and the Stahlhelm.
Modern helmets have a much wider range of applications, including helmets adapted to the specific needs of a large number of athletic pursuits and work environments, and these quite often incorporate plastics and additional synthetic materials for their light weight and shock absorption capabilities. Some types of synthetic fibres used to make helmets in the twenty-first century include Aramid, Kevlar and Twaron.
Helmets of a large number of different types have developed over the course of human history. Most early helmets had military uses, though a few might have had more ceremonial than combat-related purposes.
During the Middle Ages, a large number of different military helmets and a few ceremonial helmets were developed, almost all of these being made of metals. Some of the more important mediaeval developments included the great helm, the bascinet, the frog-mouth helm and the armet.
In the nineteenth century, more materials were incorporated, namely leather, felt and pith. The pith helmet and the leather pickelhaube were important nineteenth century developments. The greatest expansion in the variety of forms and composition of helmets, however, took place in the twentieth century, with the development of highly specialised helmets for a multitude of athletic and professional applications, as well as the advent of modern plastics. During World War I, the French army developed the Adrian helmet, the British developed the Brodie helmet, and the Germans produced the Stahlhelm.
Flight helmets were additionally developed throughout the twentieth century. A multitude of athletic helmets, including football helmets, batting helmets, cricket helmets, bicycle helmets, motorcycle helmets and racing helmets, were additionally developed in the twentieth century.
Helmets after the mid-20th century have often incorporated lightweight plastics and additional synthetic materials, and their use has become highly specialized. Some important recent developments include the French SPECTRA helmet, Spanish MARTE helmet or the American PASGT (commonly called "Kevlar" by U.S. troops) and Advanced Combat Helmet, or ACH.
As the coat of arms was originally designed to distinguish noble combatants on the battlefield or in a tournament, even while covered in armour, it isn't surprising that heraldic elements constantly incorporated the shield and the helmet, these often being the most visible parts of a knight's military equipment.
The common practise was to display a helmet as part of the coat of arms, above the shield, a practise maintained long after helmets themselves ceased to be used. In German heraldry, the helmet was even considered to be inseparable from the shield, in contrast to English heraldry, where the practise of displaying the helmet and crest alone with no shield whatsoever came into vogue in Victorian times. In most post-medieval heraldic traditions, the style, colour and position of the helmet became emblematic of the rank of the bearer. Rank was additionally often denoted by a coronet, usually either surmounting the shield or placed upon the helmet.
The practise of indicating peerage through the display of barred or grilled helmets first appeared around 1587-1615, and the heraldic convention of displaying helmets of rank in the United Kingdom, which came into vogue around Stuart times, is as follows:
- Sovereign: a gold barred-face (tournament) helm placed affronté
- Peer's helmet: silver barred-face (tournament) helm placed in profile
- Knight's or baronet's helmet: steel helm (earlier jousting helm, later close helm) placed affronté with visor open
- Esquire's helmet: steel helm placed in profile with visor closed